2026 Residents Course Complete Course Book

MASS EYE AND EAR I BOSTON, MA I JANUARY 23, 2026

Course Directors

Lindsay K. Kozek, MD, PhD and Rishi Singh, MD

Resident Coordinators

Grace Baldwin, MD and Andrew Griswold, MD, PhD

2026 Harvard Visiting Professor in Ophthalmology Jacque L. Duncan, MD

Professor of Ophthalmology, Steven G. Kramer, MD, PhD Endowed Chair in Ophthalmology, Theresa M. and Wayne M. Caygill, MD Distinguished Professor in Ophthalmology, University of California San Francisco

The complete course book is available here:

2026 HARVARD RESIDENTS’ COURSE

Degeneration and Regeneration in Ophthalmology Friday, January 23, 2026 - Mass Eye and Ear, Meltzer Auditorium 9:00 - 9:45 AM I BREAKFAST (The Sloane Teaching Room) 9:45 9:50 AM

Welcome Lindsay K. Kozek, MD, PhD

9:50 9:55 AM

Program Overview Grace E. Baldwin, MD and Andrew Griswold, MD, PhD

9:55 10:20 AM

Nature’s Band-Aid for the Eye: Harnessing Amniotic Membrane within Ophthalmology Ayush Parikh, MD and John B. Miller, MD

10:20 10:45 AM

RPE and Photoreceptor Transplantations and 3D Retinal Organoids: Where are we? Janice X. Ong, MD and Demetrios Vavvas, MD, PhD

10:45 11:10 AM

The Floppy Eyelid: Diagnosis, Associations, and Management Hueyjong Shih, MD and Michael K. Yoon, MD

11:10 - 11:30 AM I BREAK (Melzter Auditorium Hallway) 11:30 11:55 AM

Peeling Back the Layers: Turning Corneal Degeneration into Regeneration with DWEK/DSO Harold G. Dorsey, MD and Roberto Pineda, MD

11:55 AM 12:20 PM

Macular Telangiectasia Type 2: Pathogenesis and Updates on Diagnosis and Treatment Molly K.Munsell, MD and Leo Am Kim, MD, PhD

12:20 12:45 PM

Gene Therapy Associated Uveitis Andrew R. Griswold, MD, PhD and K. Matthew McKay, MD

12:45 - 1:45 PM I LUNCH (The Sloane Teaching Room) 1:45 2:10 PM

Photobiomodulation for Retinal Diseases: A Bright Idea or a False Promise? Grace E. Baldwin, MD and Rishi P. Singh, MD

2:10 2:35 PM

Hereditary Optic Neuropathies: Clinical Characteristics, Pathophysiology, and Novel Therapeutic Approaches Moosa H. Zaidi, MD and Ryan Gise, MD

2:35 3:00 PM

Beyond Intraocular Pressure: Clinical Perspectives on Neuroinflammation, Neuroprotection, and Neuroenhancement in Glaucoma Chhavi Saini, MBBS, MPH, Milica Margeta, MD, PhD and Lucy Qing Shen, MD

3:00 - 4:00 PM I BREAK & GROUP PHOTOS (Meltzer / The Ether Dome) 4:00 4:05 PM

Brief Remarks Lindsay K. Kozek, MD, PhD

4:05 4:10 PM

Introduction of Dr. Jacque L. Duncan Rachel M. Huckfeldt, MD, PhD

4:10 5:10 PM

2026 Harvard Visiting Professor in Ophthalmology Lecture High-resolution Retinal Imaging in Retinal Degenerations: New Outcome Measures for Clinical Trials Jacque L. Duncan, MD

5:10 5:15 PM

Conclusion Grace E. Baldwin, MD and Andrew Griswold, MD, PhD

Jacque L. Duncan, MD

Professor of Ophthalmology, Steven G. Kramer, MD, PhD Endowed Chairin Ophthalmology, Theresa M. and Wayne M. Caygill, MD Distinguished Professor in Ophthalmology, University of California San Francisco Chair and Distinguished Professor of the Department of Ophthalmology, University of California, San Francisco, Dr. Duncan is also the Chair of the Foundation Fighting Blindness (FFB) Scientific Advisory Board, and the co-Chair of the FFB Clinical Consortium Executive Committee. Dr. Duncan has expertise in the diagnosis and managementof patients with retinal degenerations including age-related macular degeneration, retinitis pigmentosa, cone-rod dystrophy, and Stargardt disease. Her research focuses on identifying imaging technologies to better evaluate retinal changes in disease and in response to emerging therapies.She has worked with FFB Leadership to launch the FFB Consortium which comprises over 48 clinical centers and over 160 investigators with expertise in the care and study of patients with inherited retinal degenerations.

2026 Harvard Ophthalmology Residents’ Course

Photobiomodulation Therapy for Retinal Diseases: A Comprehensive Review Grace Baldwin, MD; John B. Miller, MD; and Rishi P. Singh, MD

Abstract Photobiomodulation (PBM) is the application of low-level laser energy for treatment of medical conditions. Since the initial in the 1970s for wound healing, there has been a rapid rise in animal and clinical studies describing PBM treatment for various health conditions. The benefits of PBM for retinal diseases, important causes of vision loss, have more recently been investigated in human patients. These studies have largely focused on myopia, with a small number of studies in age-related macular degeneration (AMD) and diabetic retinopathy (DR), as well as limited, early work in central serous chorioretinopathy, inherited retinal diseases, and retinopathy of prematurity. Our review found 17 randomized controlled trials (RCTs) and 10 meta-analyses that have evaluated PBM treatment for myopia with cohorts up to just over 300 patients, while work in AMD includes six RCTs in cohorts up to 65 patients, and only one RCT in DR with 69 patients. Limitations of these studies include small to modest sample sizes, variability in PBM devices, and relatively short follow-up times of one to two years. While variability exists in the quality and size of published studies, the evidence suggests a potential clinically meaningful impact of PBM therapy for a few retinal conditions. The clinical deployment of PBM will likely be impacted by regulatory approval and reimbursement, ongoing clinical trials, and the advent of other novel treatments for retinal diseases. Further work is necessary, particularly in large cohorts with longer follow-up times, to further characterize the technology’s therapeutic potential for vision threatening diseases.

Introduction The use of light for medicinal purposes has been described since ancient times.1 Recently, light therapy, particularly with near-infrared light sources, has had an explosion of work suggesting therapeutic potential for a variety of health conditions, including inflammatory conditions, neurodegenerative diseases, cancer, and many more.2 Retinal diseases represent a significant cause of vison loss and, despite advances in treatment over the past 20 years, there remains a lack of effective treatment or prevention for many conditions.3-6 Therapeutic application of low-level laser energy, termed photobiomodulation (PBM), has recently been described for retinal conditions.7,8 PBM is an attractive potential treatment as it is noninvasive,9 has a favorable safety profile,10 and likely cost-effective, with the potential for broad dissemination.11 In this review we aim to give a comprehensive discussion of PBM for retinal diseases with a focus on the status of clinical studies performed in human patients.

The Origins of Photobiomodulation Light for medicinal purposes is by no means a modern concept.1 Historical researchers report ancient Egyptians used sun exposure to treat vitiligo over 3500 years ago.12 In the second century BC, a famous Greek physician described “heliotherapy” suggesting sun exposure may restore health.13 The ancient Greeks and Romans practiced sunbathing, and the Incas, Assyrians, and ancient Egyptians worshipped sun gods.14 In the 1800s, Florence Nightingale, considered a founder of modern nursing, described the importance of sunlight for healing.15 Light therapy in the modern era of medicine can be traced to Niels Ryberg Finsen who received the Nobel prize in 1903 for treatment of lupus with light therapy (Figure 1).16 In 1931, Trygve Gundersen, a wellregarded ophthalmologist, described light therapy for herpes keratitis.17 Invention of first visible-spectrum light emitting diode (LED) in 1962 was an important step in the advent of modern PBM devices (Figure 1).18 During that same decade, Endre Mester serendipitously discovered that 694 nm light accelerated wound healing in rodents (Figure 1).19,20 In the late 1980s, National Aeronautics and Space Administration

Baldwin, Grace (NASA) scientists incidentally discovered that LED lighting led to faster healing of hand abrasions,21 leading to NASA initiatives evaluating PBM for wound healing.22,23 With additional military funding, Quantum Devices developed a handheld portable LED, WARP 10,24 which received Food and Drug Administration (FDA) approval in 2003 for temporary relief of musculoskeletal pain (Figure 1).25

Figure 1. Historical timeline depicting the major milestones of photobiomodulation (PBM) in the last century. LED = light-emitting diode, GE = General Electric, NASA = National Aeronatics and Space Administration, AMD = age-related macular degneration, FDA = food and drug administration. In the past two decades, there has been renewed interest in the therapeutic potential of PBM across various fields of medicine26 , including orthopedics,27,28 dermatology,29,30 endocrinology,31 dentistry,32 oncology,33 cardiology,34 gynecology,35 urology,36 psychiatry,37 and neurology,38,39 among others. Evidence has emerged suggesting that PBM may have utility in retinal diseases as well,40-43 with initial animal studies reported as early as 2003,44 leading to recent clinical work and device development.45

The Biochemical Basis of Photobiomodulation in Retinal Diseases The biochemical basis for the efficacy of PBM for retinal diseases has been hypothesized based on prior work in other diseases and various animal and cellular models of retinal disease.19,20 Overall, studies suggest PBM may enable retinal recovery after damage or degeneration by (1) improving mitochondrial function, (2) reducing inflammation, and (3) increasing stem cells in retinal tissues (Figure 2).

2026 Harvard Ophthalmology Residents’ Course

Figure 2. Graphic summarizing the proposed mechanisms for the basis of PBM treatment in retinal disease. Evidence for Improved Retinal Recovery Regardless of the precise molecular mechanism, animal studies show a reduction in degeneration and improved retinal recovery after PBM treatment.46 An early study by Eells et al published in 2003 revealed that PBM attenuated the retinotoxic effects of methanol in a rat model.44 Additional animal studies have suggested that PBM helps preserve photoreceptor function, reduces retinal apoptosis, prevents rod bipolar cell depletion, and reduce retinal pigment epithelium (RPE) toxicity,47,48 evidence for which includes evaluation of retinal histopathology48 and electroretinogram (ERG) response47,49 after damage or disease.50 Animal models of retinopathy of prematurity (ROP) and DR revealed that PBM reduces neovascularization51 and capillary leakage.52 Work in animal studies of Parkinson’s disease found that PBM is protective against damage to dopaminergic amacrine cells of the retina.53 Mitochondrial Function Improves with PBM Improvement in mitochondrial function has been described as a core component of the hypothesized clinical impact of PBM across a variety of diseases,54 as supported by various animal studies.10,55-57 Mitochondria are cellular organelles that generate chemical energy in the form of adenosine triphosphate (ATP)58 for which Cytochrome c oxidase is the key enzyme.41,59 The highest density of mitochondria in the human body exist in retina photoreceptors; aging has been associated with a 70% reduction in ATP production which is thought to contribute to decline in photoreceptor function.60,61 PBM has been shown to increase cytochrome c oxidase production in cultured primary neurons.62 Likewise, various animal models of retinal disease utilizing PBM suggest it reduces oxidative stress63 and preserves mitochondrial integrity64 and function.50 Reduced inflammation after PBM PBM has also been hypothesized to have anti-inflammatory effects (Figure 2).65 This is relevant given inflammation plays a role in the pathogenesis of multiple retinal diseases.66 PBM in retinal diseases has been shown to mitigate the production of pro-inflammatory cytokines,67 protein complexes,64 and cells,68

Baldwin, Grace reduce macrophage recruitment,67 and reduce oxidative stress69 after photo-oxidative stress and in animal models of retinal disease. Stem Cell Migration and Differentiation associated with PBM Research also suggests that PBM impacts stem cell differentiation and increases the number of stem cells in retinal tissues.70,71 In an animal model of DR, PBM was shown to increase chemokines involved in stem cell migration, signaling, and differentiation.72 Additional studies have shown PBM in retinal disease models increases the number of circulating stem cells,52 enhances microglial activity,73 and enables cell cycle re-entry and dedifferentiation into a progenitor-like state in both uninjured and injured retina.74 To summarize, preclinical studies provide reasonable evidence that the biochemical basis and pathophysiology behind PBM may involve improved mitochondrial function, reduced inflammation, and enhanced stem cell recruitment, processes that are implicated in the pathogenesis of various retinal diseases (Figure 2).

Human Clinical Studies of Photobiomodulation in Retinal Diseases PBM has recently been investigated for clinical treatment of retinal diseases. Figure 3 is a graphical summary of the highest level of scientific evidence on PBM efficacy for each retinal disease, including the largest cohort size for available studies.

Figure 3. A graphic illustrating the highest level of published evidence on PBM efficacy for each retinal disease. The disease type, number of randomized controlled trials (RCT), if any, and the size of cohorts are included. AMD = age-related macular degeneration, DR = diabetic retinopathy, ROP = retinopathy of prematurity, IRD = inherited retinal disease, and CSCR = central serous chorioretinopathy. Among the studies, various PBM devices were utilized (Table 1).75 Devices can be distinguished by the utilized wavelength, power, distance from the patient’s eye, delivery mode (mask, handheld, bench top), and whether the device is experimental or commercially available, with varying levels of validation and few with formal regulatory approval.75 The results of clinical studies evaluation PBM in retinal diseases are summarized in the following sections of this review.

2026 Harvard Ophthalmology Residents’ Course

Table 1. List of photobiomodulation devices that have been used in human clinical studies for retinal diseases, including the device name, manufacturer, and wavelength.

Age-Related Macular Degeneration AMD, a progressive retinal disorder, is a leading cause of vision loss in patients older than 55 and constitutes 6-9% of global legal blindness.76,77 The prevalence of AMD is expected to rise from 196 million patients in 2020 to 288 million by 2040.76 While significant advances have been made in the treatment of exudative AMD, there is a lack of available treatment for non-exudative AMD.78 Review of the literature revealed 18 studies have investigated PBM treatment for AMD in human clinical patients, including 2 case reports,79,80 8 case series,81-88 2 prospectives studies without a control group,89,90 and 6 RCTs45,91-93 (Table 2). The earliest published study to evaluate PBM in human patients with AMD was described in 2008 (Table 2).81 Ivandic and Ivandic co-authored a publication describing treatment with an experimental 780 nm laser for both dry and wet AMD at a power of 7.5 mW in 328 eyes, they reported improved visual acuity (VA).81 It is notable, that a subsequent article by the same group, evaluating PBM in glaucoma,94 was retracted due to disagreements among the co-authors regarding safety of the laser dosage.95

Baldwin, Grace

Table 2. Summary of human clinical studies in age-related macular degeneration that utilized photobiomodulation, organized by type and date, including information regarding the publication, cohort size, country, follow-up time, and device utilized. PMID = PubMed Identifier, Pts = patients, LT = LIGHTSITE, RCT = randomized controlled trial, n/a = not applicable, US = United States wks = weeks, mos = months. In 2012, Merry et al. published an abstract reporting results from the “Toronto and Oak Ridge Photobiomodulation Study in AMD” (TORPA), reporting VA and contrast sensitivity (CS) improvement of 18 patients treated with Warp10 (670 nm, Quantum Devices) or Gentlewaves (590nm, Light Bioscience).96 Further work, TORPA 2, was published in 2017 by the same group,82 which included 42 eyes with dry AMD, three week results showed improvement in VA, CS, and drusen volume.82 Among the 8 case series and 2 prospective studies published utilizing PBM in dry AMD, sample sizes have ranged from five to just over 40 eyes (Table 2). Studies describe varying results, some suggesting improvement with PBM,87,89 while others do not describe an effect,83,85,86 though results are challenging to interpret given small sample sizes, varying follow up, and lack of control group. Nearly all studies utilized the Valeda Light Delivery system (LumiThera, Inc, Poulsbo, WA, USA), with a small number of studies using other devices (Table 2). Valeda is the first PBM device to be approved by the United States Food and Drug Administration (FDA) for treatment of dry age-related macular degeneration (AMD). The device was FDA-approved in November 2024,97 and recently acquired in September 2025 by Alcon, a company that specializes in eye care products and devices.98 Valeda is a benchtop PBM device that emits non-coherent light in 590, 660, and 850 nm LEDs (Figure 4).97 The device also includes an additional amber LED (590 nm) for the purpose of alignment. The system projects a beam spot with a diameter of approximately 30 mm at the corneal plane. According to

2026 Harvard Ophthalmology Residents’ Course the device description provided as part of the FDA approval, each treatment takes a total of 250 seconds and consists of four phases.99 In Phase 1, eyes are open and pulsed amber (590 nm, 3 Hz) and NIR (850 nm, 3 Hz) LEDs are applied for 35 seconds. In Phase 2, the eyes are closed and continuous red LED (660 nm) is applied for 90 seconds. In Phase 3, the eyes are opened and pulsed amber (590 nm, 3 Hz) and NIR (850 nm, 3 Hz) LEDs are applied for 35 seconds. In Phase 4, the eyes are closed and continuous red LED (660 nm) is applied for 90 seconds.

Figure 4. Photograph with labeled components of the Valeda light delivery system. Image source and copyright: Lumithera.com, Valeda Light Delivery System. A relatively large retrospective case series of 41 eyes from 27 patients with dry AMD who received Valeda over 16 months reported improvement in VA, CS, and ERG, with no signs of phototoxicity.87 A prospective study of 20 eyes reported improvements in VA, drusen thickness, and quality-of-life scores, however geographic atrophy (GA) area was found to be increased by 0.06 mm2 at 6 months.89 Yet the author’s noted that this was far less than the mean rate of GA progression reported in available studies, 1.78 mm2/year.100 Another prospective study of 38 eyes reported temporary improvements in visual function and drusen volume, that were not sustained at six months.90 The first prospective study to utilize swept source (SS) OCT and OCT angiography (OCTA) biomarkers in PBM treatment for AMD included 25 eyes from 19 patients evaluated four weeks after treatment. 88 The study reported significant improvement in BCVA without changes in imaging biomarkers, including central macular thickness, subfoveal choroidal thickness, capillary density, and avascular areas of the superficial and deep plexus.88 The authors cautioned that the observed change in BCVA, although statistically significant, was modest and could not be attributed to PBM in the absence of a control group; however, the short-term safety of PBM treatment was supported by the stability of SS-OCT and SS-OCTA.88 To date, six RCTs have been published evaluating the effects of PBM in AMD (Table 2).45,91-93 The LIGHTSITE trials arguably represent the most notable RCTs to date. LIGHTSITE I (LTI) was published in 2020 and included 24 eyes that received PBM with LumiThera compared to controls.93 Results showed an improvement in VA by eight letters after initial treatment, as well as significant improvements in CS, central drusen volume, central drusen thickness, and quality of life.93

Baldwin, Grace

The follow-up study, LIGHTSITE II (LTII), enrolled 53 eyes with dry AMD and found significant improvement in BCVA at nine months with a 4-letter gain in the PBM-treated group versus a 0.5-letter gain in the sham-treated group.101 Authors note that LT II was impacted by the global pandemic, resulting in limitations in study size, alterations in treatment intervals, and incomplete dosing, however the underlying results were still considered to reflect clinical safety and efficacy of PBM.102 Most recently, the LIGHTSITE III (LTIII) trial, published in 2024, evaluated 148 eyes from 100 patients randomized to receive PBM (91 eyes) or sham treatment (54 eyes).45 Subjects were enrolled across 10 centers throughout the United States. PBM was delivered in a series of nine sessions over 3-5 weeks, spaced every four months over 2 years. In terms of vision gains, approximately 55% of PBM-treated eyes showed a 5-letter gain compared with 40.8% of sham; 26.4% of PBM-treated eyes showed a 10 letter gain compared with 14.9% of sham; and 5.5% of PBM-treated eyes showed a 15 letter gain compared with 1.9% of sham.45 While there was no change in subRPE macular drusen volume in PBM treated eyes, there was an increase in the sham group. In the PBM group, subjects with higher BCVA scores showed lower values for macular drusen volume. The PBM group also showed a significant decrease in new onset GA.45 There was a favorable safety profile without notable adverse events.45 Aside from the LIGHTSITE trials, three other RCTs have been published (Table 2). A study in 2018 evaluated 60 patients with AMD, half of whom received PBM; results did not show a substantial effect on the progression of early AMD over 12 months.92 Of note, this group utilized a 505 nm LED sleep mask.92 An RCT in Italy described PBM using a 630 nm experimental device, resulting in VA improvement without change in anatomic parameters.91 A study in 2024 was performed utilizing another PBM device, EYELIGHT, which emits 590 and 630 nm light, among 142 eyes they described improvement in BCVA.103 Mean drusen volume increased significantly in the sham group, by an average of 0.25 mm,103 however the reduction in mean drusen volume by −0.97 mm3 in the PBM group was not statistically significant and there was no significant difference in central subfield thickness (CST).103 A recent meta-analysis combined the cohorts from the three LIGHTSITE trials45,93,101 for a total of 247 eyes, including pooled analysis, and showed that PBM resulted in significantly improved BCVA and reduced drusen volume.104 However they performed a minimal clinically important difference analysis, suggesting that the results did not translate into clinically significant benefits, which they defined as improvement of 6.8 ETDRS letters.104 There have been no treatment-associated adverse events reported by the published RCTs, however some case series and reports have suggested that PBM may be associated with PED rupture.79,89 In a prospective study of 20 patients treated with PBM, one patient had a drusenoid PED rupture after PBM.89 Another case report described collapse of a PED in a patient after PBM, which resulted in complete RPE and outer retinal atrophy and worse VA; the author’s suggested that PBM may have accelerated the lesion's natural history toward atrophic evolution.79 However, it is important to evaluate these case reports with caution, given similar reports have been described of spontaneous collapse of PED not associated with PBM treatment, but rather as part of an atypical natural history for AMD.105 In short, the most robust evidence to date, the LIGHTSITE trials, suggest promising evidence that PBM has potential for some improvement in vision and disease stabilization in patients with AMD, limited by a small to modest cohort size. Review of additional case series, case reports, and other studies suggest limited adverse effects with some conflicting evidence on outcomes. Larger studies are necessary with longer follow-up times.

Myopia Myopia has had a staggering increase in prevalence in the past 30 years, with some estimates that by 2050, half of the world’s population will have some degree of myopia.106 Patients with myopia have an increased risk of ocular comorbidities that can lead to vision loss, including retinal detachment, myopic degeneration, glaucoma, amblyopia, and early cataract formation.107 Because of this, significant effort has

2026 Harvard Ophthalmology Residents’ Course been directed towards therapies that may reduce the onset and progression of myopia.108 Low-energy red light therapy, PBM, has emerged as a potential intervention 109-111 A notable study in 2018 reported that PBM in rhesus monkeys reduced their axial length.110 These and other animal studies laid the ground work for the hypothesis that PBM could act to prevent myopia progression.112 The mechanism by which PBM treatment reduces AL progression is not fully understood, however evidence suggests that it is likely related to changes occurring at the level of the choroid. Studies suggest AL is negatively associated with subfoveal choroidal thickness, which has been shown to be increased by PBM in multiple studies.113-115 Compared to PBM use in other retinal diseases, a relatively substantial number of clinical studies have been published on PBM for myopia treatment and prevention.116,117 These include initial small clinical studies, randomized controlled trials (RCTs), studies evaluating impact on OCTA biomarkers, and recently published meta-analyses that evaluate PBM alone, as well as studies that compare it to other existing myopia treatments (Tables 3 and 4). Overall, the results are compelling and show promising evidence that PBM acts to slow myopia progression without adverse effects.

Table 3. Summary of randomized controlled trials in myopia that utilized photobiomodulation, organized by date, including information regarding the publication, cohort size, country, follow up time, and device utilized. PMID = PubMed Identifier, n/a = not applicable, US = United States, mos = months.

Baldwin, Grace

Table 4. Summary of meta-analyses in myopia that utilized photobiomodulation, organized by date, including information regarding the publication, studies involved, cohort size, follow up time, and average change in axial length reported. PMID = PubMed Identifier, mos = months, AL = axial length, mm = millimeters. The first published study was a RCT evaluating treatment of PBM for myopia progression prevention in children in 2021 (Table 3).118 The study compared 74 children who underwent PBM to a similar sized cohort of children who either wore Orthokeratology (OK) lenses or wore single-vision distance spectacles.118 OK lenses are a non-surgical, reversible vision correction method that involves wearing special rigid gas-permeable contact lenses overnight to temporarily reshape the cornea.119 After a follow up time of six months, axial elongation decelerated among eyes treated with PBM.118 A larger study was then published in 2022, including 246 children randomized to receive PBM.120 Compared to the control group, PBM was found to reduce axial elongation by 0.26 mm and spherical equivalent (SER) by 0.59 diopters (Table 3).120 To date, at least 17 RCTs have been performed evaluating PBM treatment for myopia progression; all studies, except one,121 were performed in China (Table 3).118,120,122-135 The primary endpoints of such studies are typically SER and axial length (AL). The RCTs utilized a variety of PBM devices, however the most common was Eyerising (Suzhou Xuanjia Optoelectronic Technology Co., South Yarra, Australia) with a wavelength of 650 nm and power of 2.0mW (Figure 5).136 The device is intended for use at home twice a day, three minutes each time. According to Eyerising international, the device is actively being used in at least 20 countries in Europe, the Middle East, and Asia.137 The Eyerising device has not been approved by the FDA for use in the United States. Of note, while existing patients in China using Eyerising are allowed to continue use, the company has responded to stricter reclassification of red-light therapy devices in China.75 Specifically, the Eyerising was recently re-classified in China from Class II to a Class III device,138 considered higher risk and required additional regulatory approval and data to prove safety and efficacy.139

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Figure 5. Photograph with labeled components of the Eyerising myopia treatment photobiomodulation device including (A) device with labeled components (B) start screen, and (C) target that patients visualize during treatment. Image Source and Copyright: Eyerising International. The largest RCT evaluating PBM in myopia to date was published in 2024 by Cao et al in JAMA Ophthalmology.132 The study included 336 children, of which 161 received PBM vs. 152 control patients.132 After one year, PBM treatment was associated with reduced SER (-0.89 D) and AL (-0.37 mm), without any appreciable adverse events.132 Of note, AL was measured with optical biometry (Lenstar LS 900; HAAG-STREIT AG), refractive error with autorefraction (ARK-510A; NidekCoLtd), and choroidal thickness with enhanced-depth imaging (SpectralisHRA+OCT;Heidelberg Engineering). Similar findings have been demonstrated across the published RCTs (Table 3). The published RCT studies have not reported serious adverse effects. Of note, one exclusion parameter is duration of afterimage post treatment. After treatment, children are asked to close their eyes until the bright spot, afterimage, disappears. If the afterimage duration exceeds 6 minutes, the child was clinically considered too sensitive to the intervention and excluded; a RCT found 2/278 children had such a reaction.127 This afterimage thus is not an adverse effect, but rather an exclusion criteria that suggests some children may react differently to the treatment. Multiple meta-analyses have also been published combining the results of various studies utilizing PBM for myopia treatment, including the aforementioned RCTs, as well as cohort studies (Table 4).114,140-148 Three meta-analyses have combined results of only RCTs (Table 4),114,141,142,147 the largest was recently published in 2025 and included a total of 1,478 children from 8 different RCTs, of which 788 received PBM treatment.114 This study found a reduction of SER by 0.49 and AL by 0.24 mm at one month.114 The other published meta-analyses have found similar reductions in AL (Table 4). Another large meta-analysis included 1,714 children of whom 824 received PBM; they found the pooled effect size for AL reduction was 0.953.146 Various meta-analyses have also been performed combining RCT and cohorts studies across a variety of different myopia treatments.149 For example, a meta-analysis included 41 RCTs evaluating myopia treatment of which 12 utilized PBM.150 Their analysis suggested that PBM decreased AL at one year by 0.31 mm, which was more effective than the other myopia treatments, including OK lenses, 0.01% atropine, or both.150 Another meta-analysis found near identical findings; they included 74 RCTs involving 12,154 participants, and found PBM reduced myopia by -0.33 mm, which was more than that of OK

Baldwin, Grace lenses, atropine, or various myopia treatment glasses.151 Other meta-analyses have described similar findings, that PBM is either as effective or the most effective myopia treatment.152-156 Especially given the risks associated with OK lenses which can lead to permanent corneal opacities, infections, and potentially devastating visual outcomes in children,157 the fact that PBM may be a non-invasive treatment with few adverse effects that is equally if not more effective that current treatments is appealing. In the end, combination therapies of myopia prevention may be more effective than a single therapy.145,158 A meta-analysis found that myopic children who received PBM in addition to standard myopia management, such as atropine, demonstrated a slower progression of myopia compared to the control group.145 Another study found that among 380 children, combination therapy of Defocus incorporated Multiple Segments (DIMS), a type of spectacle lens designed to slow the progression of myopia, with PBM had significantly greater effect in controlling myopia progression.113 Further studies may reveal nuances in how patients respond to treatment. For example a retrospective study of 323 children revealed PBM treatment resulted in more obvious AL change among patients with longer baseline AL, higher SER, thinner subfoveal choroidal thickness, older age, and with combination of other myopia prevention measures.159 Multiple studies have also investigated the impact of PBM on myopia and evaluated OCTA biomarkers. Various studies have suggested PBM increases choroidal thickness,160,161 while other retinal structures appear unchanged, including nerve fiber layer, ganglion cell layer, and central retinal thickness,162 with no significant effect on macular microcirculation.161 Another study found retinal fovea perfusion density transiently increased five minutes after PBM, but then returned to baseline.163 One study found that superficial retinal vascular density decreased in the PBM group with a statistically significant difference before and after treatment. 162 A recently published study in 2025 evaluated PBM treatment in 52 children as well as cone photoreceptor density using high-resolution adaptive optics scanning laser ophthalmoscopy (AOSLO).164 They found PBM users showed decreased cone density within 0.5-mm eccentricity from the foveal center, most notably in the temporal region. Eleven eyes exhibited abnormal low-frequency, high-brightness signals near the fovea.164 They also reported a participant had relatively small cystoid abnormalities on OCT in the ganglion cell layer, which resolved three months after discontinuing PBM therapy.164 They concluded that PBM for at least one year was associated with reduced cone density in the paracentral fovea and other subtle retinal abnormalities in some children receiving the therapy.164 In short, the consensus of OCT and OCTA studies of PBM for myopia suggest transient changes in foveal microvasculature and potentially more long-term changes in choroidal thickness, with minimal, but some, evidence of abnormal retinal morphology. However further work with longer time intervals is necessary. Continued evaluation of novel myopia treatment with advanced imaging technology such as wide-field OCTA would be valuable. Limitations of the published work to date include the fact that all the RCTs, except one, were performed in a single country; therefore, it is unclear how the technology may differ in more heterogeneous populations. However, a recently published RCT in Australia described similar findings for myopia control at a three month evaluation of an ongoing study among 34 patients (Table 3).121 With broader utilization, there may be variable treatment outcomes. Animal studies have suggested differences in PBM response among pigmented and non-pigmented fundi.165 Given the novelty of PBM devices, the follow up time for all studies is typically six months to one year, with the most being two years, therefore it is unclear whether PBM treatment will continue to prevent myopia progression in longer follow up periods. The published studies have utilized different devices with various parameters, not all of which are commercially available, which may limit repeatability. Yet most devices appear to have similar outcomes. In summary, work evaluating myopia treatment for PBM, including 17 RCTs with cohort sizes larger than 300 children, meta-analyses with over 1000 children, and studies comparing PBM to other myopia treatments, suggest PBM offers an effective means of reducing AL with few, if any, reported adverse effects. Most of the work has been performed in a single country, therefore multi-center studies in other countries are important for continued evaluation of the treatment. A single, multi-center RCT that includes different myopia treatments, including PBM, would be valuable as well as a direct comparison of different PBM devices.

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Diabetic Retinopathy Diabetic retinopathy (DR) is the fifth leading cause of blindness worldwide;166 50-75% of people with diabetes mellitus are affected by DR.167 Globally, the number of people with diabetes mellitus has quadrupled in the past three decades168 and the World Health Organization estimates that 191 million people will be living with DR in 2030.169 Diabetic macular edema (DME), a vision-threatening manifestation of DR, is characterized as retinal thickening and hard exudates, and can occur in any stage.170 DME is the most common cause of vision loss in Type 2 Diabetes.171 The prevalence of DME increases with duration of disease and stage of DR, approaching 30% in adults who have had diabetes for ≥ 20 years and 71% of those with proliferative DR.172 PBM has been proposed as potential treatment for DR, specifically DME (Table 5). A small study in 2014, found that among four eyes with center-involving DME, PBM resulted in reduction in OCT measured macular thickness (Table 5).173 They found that regions corresponding to thickened areas on OCT reduced by an average of 20% in all treated eyes, while untreated fellow eyes had an increase in retinal thickness on average of 3%.173 VA before and after appeared similar, but they did not perform a statistical analysis.

Table 5. Summary of human clinical studies in diabetic retinopathy that utilized photobiomodulation, organized by date, including information regarding the publication, study type, cohort size, country, follow up time, and device used. PMID = PubMed Identifier, RCT = randomized controlled trial mos = months, wks = weeks, pts = patients, US = United States. Of note, during the study, one patient developed sectoral optic nerve hyperemia and edema in the treated eye, consistent with non-arteritic ischemic optic neuropathy (NAION).173 It was noted that prior to the study the patient had possible pre-disposing risk factors in addition to diabetes, including hypertension and a small cup-to-disc ratio.173 However despite the development of NAION, the patient was still noted to have improvement in DME in the treated eye without improvement in the fellow eye.173 Another small study in 2017, published as a conference abstract, described improved VA and CST among six patients treated with PBM, compared to 4 controls.174 Subsequently, a study in 2020 treated 21 eyes with PBM who had DME.63 Patients received 12 sessions of PBM over 5 weeks for 90 seconds per treatment at a setting of 25, 100 or 200 mW/cm2 with Warp 10 (670 nm).63 Patients were followed up at two and six months. The study found that there was significant reduction in central macular thickness at two months by an average of 59 μm and at six months ranging from 53-129 μm depending on the treatment setting (25, 100, or 200 mW/cm2).63 There was a transient improvement in BCVA by four letters from baseline to month two, however, the overall VA gain was not sustained at month six.63 Another small study of 20 eyes of 12 patients suggested VA and retinal improvements of DME treated with an experimental device.175 ETDRS BCVA at one year was significantly improved, 20/32 to 20/25

Baldwin, Grace Snellen equivalent.175 Maximum retinal thickness was also found to be significantly reduced, 390.95 to 354.13 μm and at the fovea from 287.00 to 265.63 μm.175 In 2022 the Diabetic Retinopathy Clinical Research (DRCR) Retina Network completed an RCT of PBM therapy for center-involved DME.176 The study included 135 eyes which were randomly assigned to twicedaily treatment with either a 670-nm LED eye patch or placebo.176 At four months, there was no significant change in CST or VA.176 The results suggested PBM was safe but not effective compared to placebo. Limitations included the small sample size, however some experts suggest that the trial was sufficient to suggest there does not appear to be a benefit to eyes with DME and thus efforts should focus on other innovative and non-invasive treatment methods.177 However, it is important to note that the study used Retilux, which is distinct from the PBM device used by the recently published AMD trials – Valeda.176 Retilux is an eye mask that delivers 670 nm light through the eyelid, unlike Valeda which is a bench top system that delivers the treatment with eyes intermittently open, where the beam hits the cornea first, not the eyelid, and delivers 590, 660, and 850 nm light (Table 1, Figure 3). In fact, there has been no study evaluating DME treatment with Valeda. In short, published work evaluating PBM for DR are limited to only five studies, for which sample sizes are small. Small case series suggest a positive impact of PBM, however the largest RCT to date, which included 69 eyes, did not show a significant difference. Therefore, future work may be needed to further characterize PBM treatment for DME, particularly using other light therapy devices, such as the Valeda system.

Retinitis Pigmentosa Retinitis pigmentosa (RP) is a group of inherited retinal diseases (IRD) associated with progressive vision loss, characterized by diffuse progressive dysfunction of rod photoreceptors with subsequent degeneration of cone photoreceptors and the RPE.178 Visual impairment includes night blindness and progressive visual field loss. A few small studies have been performed in RP with PBM (Table 6). A 2022 study described 670 nm PBM preserved cone photoreceptors in an animal model of RP; motivated by the safety and efficacy, they rapidly translated the technology to a clinical study of patients with advanced RP (Table 6).179 They enrolled 12 patients that had progressed to tunnel vision and impairment of cone‐derived VA.179 Results revealed on average VA recovery of 5.4 letters at 1 month.179 There was no significant change in ERG amplitude.179 A case report described similar results; however was subsequently withdrawn at the request of the editor.180

Table 6. Summary of human clinical studies in various retinal diseases that utilized photobiomodulation, organized by date, including information regarding the publication, study type, cohort size, country, follow

2026 Harvard Ophthalmology Residents’ Course up time, and device used. Note: This table does not include studies performed in myopia, age-related macular degeneration, and diabetic retinopathy, as those are described in prior tables. PMID = PubMed Identifier, RCT = randomized controlled trial, mos = months, wks = weeks, pts = patients, UK = United Kingdom. The most recent study evaluating PBM in RP patients was published in 2024; it included 24 eyes of 12 patients treated with Valeda.181 The patients received nine treatments over a 3-week period, with three sessions per week; follow up occurred one month after intervention and each treatment session lasted approximately 5 minutes per eye.181 They described a statistically significant improvement in VA 0.62 to 0.53 logMAR (Snellen equivalent 20/83 to 20/68), without adverse results on OCT or ERG.181 Visual field improvement was also noted. Pattern Standard Deviation (PSD) and Fundus Perimetry Deviation Index (FPDI) parameters exhibited improvements from −19.87 dB to −19.45 dB on Mean Deviation, 9.77 dB to 9.76 dB on PSD, and 37% to 39% on FPDI.181 Further studies are necessary to further evaluate PBM treatment for IRD.

Stargardt Disease Stargardt disease is an IRD that causes vision loss in children and young adults.182 The disease progression is slow, but nearly all affected individuals ultimately experience severe visual disability between their 4th and 7th decade.183 A case series reported on 90 eyes of patients with Stargardt disease treated with PBM (Table 6). They utilized PBM glasses, 650 nm for 10 minutes a day, twice a day, 5 days per week for 1 year.184 BCVA, microperimetry, and pattern ERG significantly improved at 1 year.184 BCVA specifically improved from 0.7 LogMAR VA (Snellen equivalent 20/100) to 0.4 LogMAR VA (20/50).184 This study showed promising results, though findings are tempered by a relatively small sample size. On the other hand, despite being a rare disease, the study had a similar cohort size to some of the largest AMD studies. Patients were not stratified by different ages and onset of the disease; in addition there was no OCT evaluation performed, which may have gleaned useful data.184 Nonetheless, based on this initial study, PBM appears promising treatment for Stargardt disease with few to no potential adverse effects; future work is important.

Central Serous Chorioretinopathy Central serous chorioretinopathy (CSCR) is the fourth most common retinopathy after AMD, DR, and branch retinal vein occlusion.185 A case report described CSCR treatment with PBM; the patient had several small PEDs around the macula in the right eye and a giant macular serous PED with subretinal fluid in the left eye (Table 6).186 After weekly PBM for one month, followed by one session bi-weekly for 2 months, OCT of the left eye showed a gradual flattening of the macular PED at 3 months, with a complete regression at 6 months, as well as regression of subretinal fluid at 6 months. VA improved from 20/80 to 20/25.186 Another case report described a 38-year-old woman with CSCR treated with nine PBM sessions, resulting in resolved fluid; follow up at one year revealed stable vision and lack of fluid.187 The major limitation of both these case reports is that the natural history of CSCR can also include spontaneous regression. Nonetheless, further work to evaluate PBM treatment for CSCR may be valuable.

Retinopathy of Prematurity Retinopathy of prematurity (ROP) is a vaso-proliferative disorder that affects premature infants who are born before the retinal vessels complete their normal growth.188 PBM animal studies of ROP suggest that PBM acts to reduce neovascularization, vaso-obliteration, and abnormal peripheral branching patterns of retinal vessels, inspiring human clinical work.51 The first published study of PBM for ROP patients was an RCT in 2020 (Table 6).189 The study included 86 neonates randomized to receive PBM, and results showed that there was no difference in severity of ROP or requirement for laser treatment at 5 months.189 There were no adverse outcomes.189 Of note the device was not an eyemask, but rather a 670 nm light placed above the isolette.189 A major limitation of the study is that it was not powered to show a difference, for example in order to show a reduction in severe ROP the study would need to include 700

Baldwin, Grace neonates.189 Future work, particularly in countries with higher rate of ROP may be helpful in further assessing the potential therapeutic impact.190-193

Discussion: Future Work and Limitations of Photobiomodulation In this review, we comprehensively summarized and analyzed the human clinical studies that have utilized photobiomodulation for retinal diseases. While significant variability exists in the quality and size of published studies and devices used, the evidence overall suggests a potential clinically meaningful impact of PBM therapy for retinal conditions (Figure 5, Table 7). By far the largest clinical data is for treatment of myopia, and although far less work has been done in AMD, results are promising. Small studies have been described in DR, ROP, IRD, and CSCR. While additional work is necessary to further quantify the impact and clarify which patients among each disease are the best candidates, overall current scientific evidence suggests potential positive impact on functional and structural outcomes, without significant risks or adverse outcomes.

Table 7. Summary of human clinical studies in across retinal diseases that utilized photobiomodulation, comparing the number of studies in each category, the earliest study published and the largest published randomized controlled trial (RCT). Note for myopia, only meta-analyses and RCTs were included in the table. AMD = age-related macular degeneration, DR = diabetic retinopathy, RP = retinitis pigmentosa, CSCR = central serous chorioretinopathy, ROP = retinopathy of prematurity. Applications in Other Retinal Diseases There are many retinal diseases for which PBM has not been investigated, such as vitreous syneresis, epiretinal membrane, retinal vein occlusion (RVO), proliferative vitreoretinopathy (PVR), choroidal neovascularization (CNVM), myopic degeneration, radiation retinopathy, additional IRDs, uveitis and scleritis, healing after vitreoretinal procedures or surgery, and many others. Of note, an ongoing clinical trial is investigating PBM treatment for macular edema in RVO (NCT04847869, NIRVO) in Australia. Given PBM assists in wound healing it may aid in general tissue healing after ophthalmic injuries and surgery.194 For example, an animal study found that PBM at 670 nm light reduced epithelial-mesenchymal transition of RPE cells stimulated by TGF-β1, thought to play a role in development of PVR.195 OCTA evidence from the substantial work in myopia treatment provides evidence for changes occurring at the level of the choroid. It is conceivable that after RD repair, application of PBM could assist in retinal healing and further bridge the gap between anatomic success and functional outcomes.196 It may even aid in preventing inflammation after common eye surgeries such as cataract surgery, as well as novel techniques, such as suprachoroidal gene therapy197 and submacular surgery.198,199 Clinical Feasibility, Access, & Cost Access, equity, and cost are important considerations for PBM. The Current Procedure Terminology (CPT) for a single session of PBM of the retina, 0936T, was introduced on January 1, 2025.200 The International Classification of Diseases (ICD-10) codes that would support payment for PBM include those pertaining to non-exudative AMD (H35.311 – H35.3132). However Centers for Medicare & Medicaid Services (CMS) did not establish a rate in the CY 2025 Medicare Physician Fee Schedule

2026 Harvard Ophthalmology Residents’ Course (MPFS).200 Thus at this time, most patients assume full financial responsibility for the charge,200 with some Ophthalmology offices offering PBM for approximately $2,500 for 9 treatments per eye.201 The type of practitioner that is able to administer PBM varies by state laws and regulations that define the roles and responsibilities of healthcare workers.202 For example, in California, optometrists are permitted to administer PBM, but nurse practitioners, physician assistants, and medical assistants cannot.202 Currently, physicians cannot file claims for 0936T if they did not personally perform the procedure.203 Before a physician orders PBM, an eye exam with dilation is required to establish medical necessity for the procedure.202 The cost to purchase a Valeda Light Delivery System is not publicly disclosed, as pricing for professional medical equipment is typically negotiated directly with the manufacturer or authorized distributors; there does not appear to be a click cost.204 In short, any change to insurance reimbursement for PBM devices is likely to have a profound impact on access and hopefully will be directly tied to scientific evidence, equity, and access. There is a balance between expanding access to a non-invasive intervention, while ensuring safety and adequate management by a well-trained clinician. If current PBM device manufacturers and clinicians continue to make PBM treatment cost prohibitive to the public, it may result in off market companies or home devices that have not passed the clinical regulatory process.

Figure 6. Graphic illustrating factors that may impact the future of photobiomodulation and the limitations associated with current evidence for photobiomodulation. Future Work The future of PBM for retinal diseases will likely be impacted by clinical regulatory approval, ongoing and future clinical trials in retinal diseases, device development, as well as other novel treatments for retinal diseases (Figure 6). Additional research may consider combining PBM with existing treatment, for example AREDS-2 vitamins, and other future treatments such as novel vitamin, antioxidants, and statins,205-207 as well as existing and novel therapeutics, such as photodynamic therapy,208 subthreshold laser209-213 and gene therapy.214 Indeed, animal models have revealed potential synergistic effects of combining PBM with vitamins thought to reduce retinal inflammation.57,215-220 As our understanding of retinal disease pathogenesis continues to evolve, such as research into plasma-based metabolomics biomarkers,221 the advent of novel disease targets may have a synergistic effect with PBM.

Baldwin, Grace Future research in other retinal diseases may consider combining novel imaging biomarkers and functional endpoints222 to further characterize the structural and functional changes occurring with PBM therapy. While there has been work evaluating OCTA biomarkers in myopia, little analogous work has been done in AMD88 or other retinal diseases. Current PBM devices use a wavelength from 670-800 nm, however it is possible further work may elucidate the precise wavelength and power needed for specific diseases, which may enable more targeted treatment.223 Further work is needed to determine the most effective mode of treatment, both for therapeutic delivery and compliance. The growing utilization of telemedicine,224 particularly for retinal imaging, could also potentially have a synergistic relationship with PBM, including the advent of home PBM devices. Limitations Despite promising data there are significant limitations regarding the evidence for PBM (Figure 6). A major limitation is that the sample sizes for PBM studies in retinal diseases are quite small and most studies lack a control arm. On the other hand, the largest RCTs that exist, such as those for AMD and myopia, suggest a positive impact on VA and retinal structure. Evidence is also limited by the relatively short follow up time, often 3-6 months, sometimes 1-2 years maximum. As the literature develops, published work should focus on larger sample sizes, as small studies and case reports likely lead to significant bias and may build a murkier picture of scientific evidence. Another limitation is the lack of diversity of the study cohorts. Work using Valeda in AMD is skewed towards white individuals. In fact, the FDA approval document for Valeda reports that no non-white subjects received treatment which may limit safety and efficacy in a diverse population.97 Similar issues with homogeneity exist in the myopia data, as all RCTs except one were performed in China. Further work in diverse cohorts of patients is necessary with special attention to the age, gender, and racial and ethnic backgrounds of the participants The data for PBM is also limited by variability in how the diseases are defined and end points, and whether the results are clinically meaningful and impact quality of life. There is also significant variability in devices used across studies and their validation.11 For example, a study evaluated two devices that had been used in myopia treatment, Sky-n1201a and Future Vision, and found three minutes of continuous viewing approached or surpassed the maximum permissible exposure, theoretically putting the retina at risk for photochemical and thermal damage.75 The precise dosage of light and how patients may respond is variable,85 thus personalized treatment protocols may emerge in the future.225 For example, some work suggests degree of fundus pigmentation and degree of retinal damage may impact response to PBM treatment.165,226

Conclusion In conclusion, PBM is a novel non-invasive treatment being investigated for a variety of retinal conditions. While current scientific evidence has major limitations of small sample sizes and study variability in devices and endpoints, the evidence generally points toward a positive clinical impact without significant risk, particularly in myopia and potentially in AMD. Where the future of PBM and its integration with the ongoing rapid innovation in retinal therapeutics may lead is unknown. Nonetheless, current evidence suggests continued investigation with larger, rigorously designed clinical studies is warranted and important.

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2026 Harvard Ophthalmology Residents’ Course 150. Lee SH, Tseng BY, Wang JH, Chiu CJ. Efficacy of Myopia Prevention in At-Risk Children: A Systematic Review and Network Meta-Analysis. J Clin Med. Feb 28 2025;14(5)doi:10.3390/jcm14051665 151. Zaabaar E, Zhang XJ, Zhang Y, et al. Light exposure therapy for myopia control: a systematic review and Bayesian network meta-analysis. British Journal of Ophthalmology. 2024;108(8):1053–1059. doi:10.1136/bjo2023-323798 152. Zaabaar E, Asiamah R, Kyei S, Ankamah S. Myopia control strategies: A systematic review and meta-metaanalysis. Ophthalmic Physiol Opt. Jan 2025;45(1):160–176. doi:10.1111/opo.13417 153. Lawrenson JG, Huntjens B, Virgili G, et al. Interventions for myopia control in children: a living systematic review and network meta-analysis. Cochrane Database Syst Rev. Feb 13 2025;2(2):Cd014758. doi:10.1002/14651858.CD014758.pub3 154. Fan H, Yu J, Jiang A, et al. Effects of repeated low-level red light therapy on myopia progression in children: a systematic review and meta-analysis. Front Med (Lausanne). 2025;12:1640403. doi:10.3389/fmed.2025.1640403 155. Jung S, Eom Y, Song JS, Hyon JY, Jeon HS. Clinical Features and Visual Outcome of Infectious Keratitis Associated with Orthokeratology Lens in Korean Pediatric Patients. Korean J Ophthalmol. Oct 2024;38(5):399– 412. doi:10.3341/kjo.2024.0101 156. Zhang G, Jiang J, Qu C. Myopia prevention and control in children: a systematic review and network metaanalysis. Eye (Lond). Nov 2023;37(16):3461–3469. doi:10.1038/s41433-023-02534-8 157. Peng Y, Wang D, Ma N, Jie H. Exploration of correlated factors of axial length changes after repeated low-level red-light irradiation in the real world. BMC Ophthalmol. Oct 1 2025;25(1):530. doi:10.1186/s12886-025-04379-z 158. Zhao C, Ni Y, Zeng J. Effect of red-light therapy on retinal and choroidal blood perfusion in myopic children. Ophthalmic Physiol Opt. Nov 2023;43(6):1427–1437. doi:10.1111/opo.13202 159. Liu L, Wang Y, Liu F, et al. Effects of repeated low-level red-light therapy on macular retinal thickness and microvascular system in children with myopia. Photodiagnosis Photodyn Ther. Feb 2024;45:103938. doi:10.1016/j.pdpdt.2023.103938 160. Ren J, Xu JN, Liu YZ, Gu XL, Wang Y. Short-term effectiveness and safety of photobiomodulation on low-tomoderate myopia. Lasers Med Sci. Feb 15 2025;40(1):95. doi:10.1007/s10103-024-04119-7 161. Yang W, Lin F, Li M, Wei R, Zhou J, Zhou X. Immediate Effect in the Retina and Choroid after 650 nm Low-Level Red Light Therapy in Children. Ophthalmic Res. 2023;66(1):312–318. doi:10.1159/000527787 162. Liao X, Yu J, Fan Y, et al. Cone Density Changes After Repeated Low-Level Red Light Treatment in Children With Myopia. JAMA Ophthalmol. Jun 1 2025;143(6):480–488. doi:10.1001/jamaophthalmol.2025.0835 163. Ao J, Chidlow G, Wood JPM, Casson RJ. Safety Profile of Slit-Lamp-Delivered Retinal Laser Photobiomodulation. Transl Vis Sci Technol. Mar 2020;9(4):22. doi:10.1167/tvst.9.4.22 164. Burton MJ, Ramke J, Marques AP, et al. The Lancet Global Health Commission on Global Eye Health: vision beyond 2020. Lancet Glob Health. Apr 2021;9(4):e489–e551. doi:10.1016/s2214-109x(20)30488-5 165. Kempen JH, O'Colmain BJ, Leske MC, et al. The prevalence of diabetic retinopathy among adults in the United States. Arch Ophthalmol. Apr 2004;122(4):552–63. doi:10.1001/archopht.122.4.552 166. Zheng Y, Ley SH, Hu FB. Global aetiology and epidemiology of type 2 diabetes mellitus and its complications. Nat Rev Endocrinol. 2018 Feb;14(2):88-98. doi: 10.1038/nrendo.2017.151. Epub 2017 Dec 8. PMID: 29219149. 167. Ting DSW, Cheung GCM, Wong TY. Diabetic retinopathy: global prevalence, major risk factors, screening practices and public health challenges: a review. Clinical & experimental ophthalmology. 2016;44(4):260–277. 168. Kwan CC, Fawzi AA. Imaging and Biomarkers in Diabetic Macular Edema and Diabetic Retinopathy. Curr Diab Rep. 2019 Aug 31;19(10):95. doi: 10.1007/s11892-019-1226-2. PMID: 31473838. 169. Lee R, Wong TY, Sabanayagam C. Epidemiology of diabetic retinopathy, diabetic macular edema and related vision loss. Eye and vision. 2015;2(1):1–25. 170. Kim EJ, Lin WV, Rodriguez SM, Chen A, Loya A, Weng CY. Treatment of Diabetic Macular Edema. Curr Diab Rep. 2019 Jul 29;19(9):68. doi: 10.1007/s11892-019-1188-4. PMID: 31359157.

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171. Tang J, Herda AA, Kern TS. Photobiomodulation in the treatment of patients with non-center-involving diabetic macular oedema. Br J Ophthalmol. Aug 2014;98(8):1013–5. doi:10.1136/bjophthalmol-2013-304477 172. Eells JT, Gopalakrishnan S, Connor TB, et al. 670 nm Photobiomodulation as a Therapy for Diabetic Macular Edema: A Pilot Study. Investigative Ophthalmology & Visual Science. 2017;58(8):932–932. 173. Chen Z, Chen B, Hu P, Liu H, Zheng D. A preliminary observation on rod cell photobiomodulation in treating diabetic macular edema. Adv Ophthalmol Pract Res. Aug–Sep 2022;2(2):100051. doi:10.1016/j.aopr.2022.100051 174. Kim JE, Glassman AR, Josic K, et al. A Randomized Trial of Photobiomodulation Therapy for Center-Involved Diabetic Macular Edema with Good Visual Acuity (Protocol AE). Ophthalmology Retina. 2022/04/01/ 2022;6(4):298–307. doi:https://doi.org/10.1016/j.oret.2021.10.003 175. Sun JK, Glassman AR, Jampol LM. Spotlight on the DRCR Retina Network's Photobiomodulation for Diabetic Macular Edema Trial. JAMA Ophthalmol. Apr 1 2022;140(4):304–306. doi:10.1001/jamaophthalmol.2021.6331 176. Confalonieri F, La Rosa A, Ottonelli G, et al. Retinitis Pigmentosa and Therapeutic Approaches: A Systematic Review. J Clin Med. Aug 9 2024;13(16)doi:10.3390/jcm13164680 177. Casson RJ, Wood JPM, Ao J, et al. Cone photoreceptor preservation with laser photobiomodulation in murine and human retinal dystrophy. Clin Transl Med. Feb 2022;12(2):e673. doi:10.1002/ctm2.673 178. Luque-Mialdea F, Molina-Seoane V. Retinitis pigmentosa: Significant improvement with photobiomodulation. Arch Soc Esp Oftalmol (Engl Ed). Oct 7 2023;doi:10.1016/j.oftale.2023.10.001 179. Siqueira RC, Pinho TS, Brandão CC. Short-Term Results of Multiwavelength Photobiomodulation in Retinitis Pigmentosa. Clin Ophthalmol. 2024;18:3715–3724. doi:10.2147/opth.S483722 180. Britten-Jones AC, Al-Khuzaei S, Rizzi M, et al. Stargardt's Connected Research Network Inaugural Meeting: Landscape Review and Horizon Scanning of Stargardt Disease. Transl Vis Sci Technol. Sep 2 2025;14(9):26. doi:10.1167/tvst.14.9.26 181. Cremers FPM, Lee W, Collin RWJ, Allikmets R. Clinical spectrum, genetic complexity and therapeutic approaches for retinal disease caused by ABCA4 mutations. Prog Retin Eye Res. Nov 2020;79:100861. doi:10.1016/j.preteyeres.2020.100861 182. Scalinci SZ, Valsecchi N, Pacella E, Trovato Battagliola E. Effects of Photo-Biomodulation in Stargardt Disease. Clin Ophthalmol. 2022;16:85–91. doi:10.2147/opth.S344378 183. Wang M, Munch IC, Hasler PW, Prünte C, Larsen M. Central serous chorioretinopathy. Acta Ophthalmol. Mar 2008;86(2):126–45. doi:10.1111/j.1600-0420.2007.00889.x 184. Iovino C, Damiano L, Piccirillo V, Testa F, Giannaccare G, Simonelli F. PHOTOBIOMODULATION THERAPY FOR SEROUS PIGMENT EPITHELIUM DETACHMENT IN CHRONIC CENTRAL SEROUS CHORIORETINOPATHY. Retin Cases Brief Rep. Nov 1 2025;19(6):766–770. doi:10.1097/icb.0000000000001665 185. Sachdev A. Improvement in Central Serous Chorioretinopathy Following Multiwavelength Photobiomodulation Treatment - Case Report. Ophthalmol Ther. Jul 2024;13(7):2055–2060. doi:10.1007/s40123-024-00963-6 186. Bujoreanu Bezman L, Tiutiuca C, Totolici G, et al. Latest Trends in Retinopathy of Prematurity: Research on Risk Factors, Diagnostic Methods and Therapies. Int J Gen Med. 2023;16:937–949. doi:10.2147/ijgm.S401122 187. Kent AL, Abdel-Latif ME, Cochrane T, et al. A pilot randomised clinical trial of 670 nm red light for reducing retinopathy of prematurity. Pediatr Res. Jan 2020;87(1):131–136. doi:10.1038/s41390-019-0520-7 188. Chawla D, Deorari A. Retinopathy of prematurity prevention, screening and treatment programmes: Progress in India. Semin Perinatol. Oct 2019;43(6):344–347. doi:10.1053/j.semperi.2019.05.006 189. Vinekar A, Venkatesh R, Mangalesh S, Jayadev C, Shetty KB, Gilbert C. Reducing the Impact of the COVID-19 Pandemic on Retinopathy of Prematurity Screening: Successful Strategies Learnt from a Multi-Center TeleMedicine Program in India. Ophthalmic Epidemiol. Jun 2024;31(3):291–298. doi:10.1080/09286586.2023.2251147 190. Das A, Subramaniam P, Shah PK, Venkatapathy N. Prevalence of Unscreened Premature Infants Presenting With Advanced Stages of Retinopathy of Prematurity in South India: An Analysis of 220 Eyes. J Pediatr Ophthalmol Strabismus. Sep–Oct 2024;61(5):339–343. doi:10.3928/01913913-20240508-02

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191. Chan RV, Patel SN, Ryan MC, et al. The Global Education Network for Retinopathy of Prematurity (Gen-Rop): Development, Implementation, and Evaluation of A Novel Tele-Education System (An American Ophthalmological Society Thesis). Trans Am Ophthalmol Soc. 2015;113:T2. 192. Siqueira RC. Photobiomodulation Using Light-Emitting Diode (LED) for Treatment of Retinal Diseases. Clin Ophthalmol. 2024;18:215–225. doi:10.2147/opth.S441962 193. Watson O, Aggio-Bruce R, Essex R, Valter K. Effect of Photobiomodulation on Proliferative Changes in the Retina: Evidence from an In Vitro Model of PVR. Adv Exp Med Biol. 2025;1468:195–200. doi:10.1007/978-3-031-765506_32 194. Baldwin G, Finn M, Yeung T, et al. Clinical Characteristics of Reduced Contrast Sensitivity After Retinal Detachment Repair. Investigative Ophthalmology & Visual Science. 2023;64(8):2485–2485. 195. Kansara V, Muya L, Wan CR, Ciulla TA. Suprachoroidal Delivery of Viral and Nonviral Gene Therapy for Retinal Diseases. J Ocul Pharmacol Ther. Jul/Aug 2020;36(6):384–392. doi:10.1089/jop.2019.0126 196. Tripepi D, Jalil A, Ally N, et al. The Role of Subretinal Injection in Ophthalmic Surgery: Therapeutic Agent Delivery and Other Indications. Int J Mol Sci. Jun 23 2023;24(13)doi:10.3390/ijms241310535 197. Simunovic MP, Shao EH, Osaadon P, Sasongko MB, Too LK. Two-step versus 1-step subretinal injection to compare subretinal drug delivery: a randomised study protocol. BMJ Open. Dec 15 2021;11(12):e049976. doi:10.1136/bmjopen-2021-049976 198. Group CC. Reimbursement for Retinal Photobiomodulation Therapy. Accessed November 23, 2025. https://corcoranccg.com/reimbursement-for-retinal-photobiomodulation-therapy/ 199. Kent W. Small MMRI. Photobiomdulation (Red Light Therapy) Valeda® – A New Treatment for Dry Macular Degeneration. Accessed November 23, 2025. https://maculaandretinainstitute.com/photobiomodulation-red-lighttherapy/ 200. Kevin J. Corcoran C, FNAO. How to Code the Novel Treatment for AMD. Accessed November 23, 2025. https://ophthalmologymanagement.com/issues/2025/julyaugust/coding-and-reimbursement/ 201. Corcoran C. Supplemental Questions & Answers - August 14, 2025. Accessed November 23, 2025. https://myvaleda.com/wp-content/uploads/documents/us-reimbursement-resources/MKT0146_REV_B_VAL_QA_Additional_Discussion_081425.pdf 202. Valeda. Introducing the Valeda Light Delivery System. Accessed Novmer 23, 2025. https://myvaleda.com/ 203. Ibuki M, Shoda C, Miwa Y, Ishida A, Tsubota K, Kurihara T. Therapeutic Effect of Garcinia cambogia Extract and Hydroxycitric Acid Inhibiting Hypoxia-Inducible Factor in a Murine Model of Age-Related Macular Degeneration. Int J Mol Sci. Oct 11 2019;20(20)doi:10.3390/ijms20205049 204. Vavvas DG, Daniels AB, Kapsala ZG, et al. Regression of Some High-risk Features of Age-related Macular Degeneration (AMD) in Patients Receiving Intensive Statin Treatment. EBioMedicine. Mar 2016;5:198–203. doi:10.1016/j.ebiom.2016.01.033 205. Bannerman A, Choi H, Ploumi I, et al. Long-Term Use of High-Dose Statins in Eyes with Intermediate Age-related Macular Degeneration. Investigative Ophthalmology & Visual Science. 2024;65(7):4372–4372. 206. Bae SH, Heo J, Kim C, et al. Low-fluence photodynamic therapy versus ranibizumab for chronic central serous chorioretinopathy: one-year results of a randomized trial. Ophthalmology. Feb 2014;121(2):558–65. doi:10.1016/j.ophtha.2013.09.024 207. Vessey KA, Ho T, Jobling AI, et al. Nanosecond Laser Treatment for Age-Related Macular Degeneration Does Not Induce Focal Vision Loss or New Vessel Growth in the Retina. Invest Ophthalmol Vis Sci. Feb 1 2018;59(2):731– 745. doi:10.1167/iovs.17-23098 208. Guymer RH, Brassington KH, Dimitrov P, et al. Nanosecond-laser application in intermediate AMD: 12-month results of fundus appearance and macular function. Clin Exp Ophthalmol. Jul 2014;42(5):466–79. doi:10.1111/ceo.12247

Baldwin, Grace 209. Luttrull JK, Sinclair SH. Safety of transfoveal subthreshold diode micropulse laser for fovea-involving diabetic macular edema in eyes with good visual acuity. Retina. Oct 2014;34(10):2010–20. doi:10.1097/iae.0000000000000177 210. Koinzer S, Elsner H, Klatt C, et al. Selective retina therapy (SRT) of chronic subfoveal fluid after surgery of rhegmatogenous retinal detachment: three case reports. Graefes Arch Clin Exp Ophthalmol. Oct 2008;246(10):1373–8. doi:10.1007/s00417-008-0860-1 211. Tarutta EP, Iomdina EN, Akhmedzhanova EV. [Progressing myopia in children: does it need treatment or not?]. Vestn Oftalmol. Mar–Apr 2005;121(2):5–8. 212. Martinez Velazquez LA, Ballios BG. The Next Generation of Molecular and Cellular Therapeutics for Inherited Retinal Disease. Int J Mol Sci. Oct 26 2021;22(21)doi:10.3390/ijms222111542 213. Calbiague García V, Cadiz B, Herrera P, Díaz A, Schmachtenberg O. Evaluation of Photobiomodulation and Boldine as Alternative Treatment Options in Two Diabetic Retinopathy Models. Int J Mol Sci. Apr 27 2023;24(9)doi:10.3390/ijms24097918 214. Marco FD, Romeo S, Nandasena C, et al. The time course of action of two neuroprotectants, dietary saffron and photobiomodulation, assessed in the rat retina. Am J Neurodegener Dis. 2013;2(3):208–20. 215. Natoli R, Zhu Y, Valter K, Bisti S, Eells J, Stone J. Gene and noncoding RNA regulation underlying photoreceptor protection: microarray study of dietary antioxidant saffron and photobiomodulation in rat retina. Mol Vis. Sep 3 2010;16:1801–22. 216. Di Paolo M. Sequential PBM-Saffron Treatment in an Animal Model of Retinal Degeneration. Medicina (Kaunas). Oct 3 2021;57(10)doi:10.3390/medicina57101059 217. Di Marco F, Di Paolo M, Romeo S, et al. Combining neuroprotectants in a model of retinal degeneration: no additive benefit. PLoS One. 2014;9(6):e100389. doi:10.1371/journal.pone.0100389 218. Pinelli R, Bertelli M, Scaffidi E, et al. The neurobiology of nutraceuticals combined with light exposure, a case report in the course of retinal degeneration. Arch Ital Biol. Dec 31 2021;159(3-4):134–150. doi:10.12871/000398292021343 219. Laíns I, Kelly RS, Miller JB, et al. Human Plasma Metabolomics Study across All Stages of Age-Related Macular Degeneration Identifies Potential Lipid Biomarkers. Ophthalmology. 2018;125(2):245–254. doi:10.1016/j.ophtha.2017.08.008 220. Baldwin G. Evaluating the Association of Widefield Swept-Source Optical Coherence Tomography Angiography with Visual Function in Common Retinal Diseases. Harvard Medical School; 2023. 221. Chichan H, Aldujaly IH, Michalakis K, Kanal L. Photobiomodulation in ocular therapy: current status and future perspectives. Int J Ophthalmol. 2025;18(2):351–357. doi:10.18240/ijo.2025.02.20 222. Parikh D, Armstrong G, Liou V, Husain D. Advances in Telemedicine in Ophthalmology. Semin Ophthalmol. May 18 2020;35(4):210–215. doi:10.1080/08820538.2020.1789675 223. Sharma A, Wu L, Bloom S, et al. RWC Update: Photobiomodulation for Non-Neovascular AMD; High Definition TRD with NGENUITY 1.5; Retinopathy of Prematurity. Ophthalmic Surg Lasers Imaging Retina. Sep 2025;56(9):515–518. doi:10.3928/23258160-20250827-01 224. Chu-Tan JA, Rutar M, Saxena K, et al. Efficacy of 670 nm light therapy to protect against photoreceptor cell death is dependent on the severity of damage. International Journal of Photoenergy. 2016;2016(1):2734139.

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Peeling Back the Layers: Turning Corneal Degeneration into Regeneration with DWEK/DSO Harold Dorsey, MD; and Roberto Pineda II MD

Introduction Fuchs endothelial corneal dystrophy (FECD) is the most common primary corneal dystrophy in the world.1 The hallmark of this disease is the bilateral, progressive loss of corneal endothelial cells and the accumulation of guttae centrally, outgrowths of extracellular matrix that, over time, interfere with the regular endothelial cell pattern. These processes can hinder the cornea's ability to remove fluid, leading to corneal swelling and, subsequently, a decline in corneal transparency and an increase in its thickness.2 Clinically, progression of this process results in a reduction in visual acuity and can cause visual phenomena such as glare, halos, and reduced contrast. The clinical course of FECD is commonly thought to span 10-20 years, and it is a chronic degenerative disease. The total number of people worldwide over the age of 30 with FECD is estimated to be nearly 300 million 3 Although corneal edema in FECD can be partially managed with hypertonic saline eye drops or ointment, this is not a disease-modifying therapy and does not halt disease progression. 4 In the past, the only option for definitively treating FECD was full-thickness corneal transplantation via penetrating keratoplasty (PK).5 This is a complex procedure with a risk for complications during surgery, including hypotony, suprachoroidal hemorrhage, and wound leak, as well as complications during the post-operative period, such as astigmatism, graft failure/rejection, endophthalmitis, cataract formation, or discomfort/trauma from sutures. Furthermore, transplantation of all corneal layers, rather than the specific layers driving the disease, is not ideal and can result in replacement of otherwise healthy tissue. The first known selective corneal transplant was a posterior lamellar keratoplasty by Dr. Charles Tillet in 1956 for a case of FECD.6 Termed the “forgotten surgery” by some, the posterior keratoplasty was only reintroduced in year 1998 by Gerrit Melles in a human cadaver model.7 In 2004, Dr. Gerrit Melles described the technique later called Descemet's stripping endothelial keratoplasty (DSEK), in which donor tissue consisting of posterior stroma, Bowman's layer, and endothelium was transplanted to a host cornea after the Descemet's membrane and endothelium have been stripped.8 In 2006, Dr. Melles proceeded to create a technique in which the donor tissue transplanted contained only Descemet's membrane and the endothelium, named Descemet’s membrane endothelial keratoplasty (DMEK).9 From 2005 to 2014 in the United States, PK decreased from accounting for 95% of all corneal transplants to 42%, while DSEK increased to account for 50% of the corneal transplants done in 2014.10 From the years 2015 to 2020, PK volume continued to decline (40 to 36.4%); DSAEK/DSEK volume decreased as well (47% to 33.9%), while DMEK volume increased (9.8% to 27.8%).10 In the 2024 eye banking statistical reports, DMEK became the most common form of corneal transplantation (18256, 35.4%) followed by DSAEK (16,345, 31.7%), and PK (14,143, 27.4%).11 In this rapidly changing field of corneal transplantation, a new option, Descemetorhexis Without Endothelial Keratoplasty (DWEK), or Descemet's stripping only (DSO), has also become a viable management for cases of early to moderate FECD.12 In this procedure, a central area of Descemet's membrane and endothelium, including central guttae, is removed without subsequent transplantation. This relies on the corneal endothelium’s inherent regenerative capacity, as healthy peripheral endothelial cells migrate centrally over the stripped area, improving endothelial function and ultimately clarity.12 In this paper, we will discuss DWEK/DSO as a form of regenerative medicine to treat the degenerative process of Fuchs endothelial corneal dystrophy (FECD).

Dorsey, Harold

Corneal Endothelium Anatomy and Function The cornea is a layered tissue at the front of the eye that includes the epithelium, Bowman's layer, stroma, Descemet's membrane, and endothelium. The corneal endothelium is a monolayer of hexagonal cells that lines the cornea's posterior surface. There are an estimated 350,000 endothelial cells per cornea, with a cell density of about 2,500 cells/mm2 in middle-aged humans.13 These cells are mitochondria-rich and serve as active fluid transporters for the cornea, as well as a barrier to the aqueous humor.14 Loss of this key transport function can cause corneal edema, which can lead to further complications such as vision loss and bullous keratopathy. As a barrier, corneal endothelial cells use tight junctions to stop diffusion of aqueous into the corneal stroma, which is composed principally of glycosaminoglycans and must stay dehydrated to maintain corneal clarity.15 Despite this, the corneal endothelium is an imperfect barrier and, without a secondary mechanism of dehydrating the stroma, would not be able to maintain deturgescence. To assist in preventing diffusion, the endothelium uses active ionic transport via its high density of Na⁺/K⁺-ATPase pumps. The cornea depends on these pumps to maintain its dehydrated state, as studies have shown that ouabain, an inhibitor of the Na⁺/K⁺-ATPase pumps, leads to corneal stromal edema.16 The primary driver of fluid transport is the ionic gradient created predominantly by HCO₃⁻ flux. Inside endothelial cells, CO₂, along with H₂O, produces bicarbonate in a process driven by carbonic anhydrase II. The Na⁺/K⁺-ATPase produces the Na+ gradient needed to drive Electrogenic Sodium Bicarbonate Cotransporter 1 (NBCe1). This dominant bicarbonate transporter pushes HCO₃⁻ into the aqueous humor, creating a net osmotic gradient that draws water into it.16

Fuchs Endothelial Corneal Dystrophy FECD is driven by genetic and epigenetic susceptibility that culminates in the pathologic buildup of extracellular matrix components, named guttae, along with cellular apoptosis. The strongest association has been observed with trinucleotide repeats in TCF4, which lead to RNA toxicity and misplicing, affecting the cytoskeleton and hindering the structures involved in the barrier function of the corneal endothelium.17 The mutant COL8A2 gene, which is associated with alterations in endothelial cell morphology, cell loss, and basement membrane guttae, has also demonstrated an association with FECD.18 More genes involved in this disease are being discovered over time, and studies have shown that the interplay of multiple genetic risk factors can be associated with FECD and cause different phenotypes.19 A recent 2025 Nature study has demonstrated 214 differentially expressed genes (193 upregulated, and 21 downregulated) in FECD cell lines when compared to normal. Several transcriptional regulator genes (MAFB, TFAP2B, and POU6F2), were also found to be downregulated in FECD cell lines when compared to normal.20 One downstream outcome of stressed corneal endothelial cells with genetic risk factors is the formation of guttae. Guttae are extracellular masses that form on the Descemet's membrane. In the early stages of FECD, guttae are quite scattered and usually appear only in a small portion of the central corneal endothelium. As the disease progresses, they are found in increasingly large areas of the endothelium and become confluent.21 Endothelial cell apoptosis is also a hallmark of FECD, and directly impairs the function of the endothelial cell layer by depleting the number of viable cells. An increased susceptibility to oxidative stress is thought to play a significant role in endothelial cell apoptosis. Environmental and lifestyle factors, such as exposure to UV radiation and smoking, have been found to promote endothelial degeneration. Systemic conditions, such as hypertension, metabolic syndrome, and diabetes, have also been found to contribute.4 The processes of guttae formation and corneal endothelial cell apoptosis are not mutually exclusive and are likely linked.22 Recent research suggests that guttae may be toxic, or that corneal endothelial cells and/or their apoptosis could have a role in guttae formation.22 As FECD progresses, corneal deturgescence is continuously impaired, and corneal edema/thickening worsens. In the late stage, this can progress to epithelial bullae formation, which can rupture, along with subepithelial scarring and corneal neovascularization. 4

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Corneal Endothelium Regeneration Studies using transmission electron microscopy have demonstrated that endothelial cell proliferation likely ceases upon cell-to-cell contact.14 Cell density studies also demonstrate that the corneal endothelium does not replicate at a rate that would be able to sufficiently balance out endothelial cell loss (i.e., from injury or other forms of cell death).14 There is evidence that, after the third trimester of fetal development, there is no increase in endothelial cell count via cellular proliferation.14 In fact, endothelial cell density declines continuously since birth, from an average endothelial cell density of 3500–4000 cells/mm2 to 2000 2000 cells/mm2 as adults.14 In vivo studies have demonstrated that, although a small amount of corneal endothelial wound healing may occur via cellular proliferation, this process alone is inadequate to fulfill this task.23 Endothelial cell enlargement and spread to cover sites with missing endothelium have been demonstrated in vivo to be the primary mechanism by which endothelial cell repair occurs.24 It is hypothesized that the corneal endothelial cells are in a state of G1-phase arrest.14 This is likely due to a variety of mechanisms and factors. First, endothelial cell studies in rats have demonstrated a temporal relationship between the end of proliferation and the onset of endothelial cell-to-cell contact.25 Western blot studies have also demonstrated that p27Kip1 expression plays a role in endothelial cell-to-cell contact inhibition.26 However, the absence of a robust proliferative response after endothelial cell disruption trauma and disease suggests there must be other factors at hand that limit this process. Studies have demonstrated low levels of positive growth factors in the aqueous humor of normal eyes (i.e., basic fibroblast growth factor, hepatocyte growth factor, and insulin-like growth factor-I and –II).27 Furthermore, Transforming Growth Factor Beta 2 (TGF-β2) has been found to downregulate CDK4 expression, maintaining higher levels of p27Kip1, which helps keep corneal endothelial cells in the G1 phase.28 Although TGF-β2 is found in its latent form in the aqueous humor, corneal endothelial cells express thrombospondin-1, which can activate it, and also express TGF-β receptors I-III, which optimize TGF-β signal transduction.29,30

Descemet's Stripping Only (DSO)/Descemetorhexis Without Endothelial Keratoplasty (DWEK) DWEK/DSO is the removal of Descemet's layer, endothelium, and guttae without a subsequent keratoplasty to replace the missing tissue. The feasibility of this procedure was supported by multiple case reports demonstrating corneal stromal deturgescence in cases of unintentional Descemet's layer detachment, whether iatrogenic or due to failed graft-host adherence post-transplant. 31 In a 2013 prospective case series, eight consecutive patients with FECD underwent DWEK with simultaneous phacoemulsification and posterior-chamber intraocular lens implantation (PCIOL). Improved corneal clearing was noted in only three of eight patients, and only one maintained the clearance. At the time, they strongly discouraged performing DWEK in FECD.32 Unfortunately, this report was written in the form of correspondence to the American Academy of Ophthalmology journal, and does not report important commonly disclosed factors such as age and size of descemetorhexis. A 2017 case series of five eyes (five patients) with FECD demonstrated corneal clearance in four (80%) of eyes after DWEK, but only two eyes demonstrated the expected improvement in visual acuity due to astigmatism.33 In a 2016 retrospective case series of 13 eyes (11 patients) of patients with FECD who underwent DWEK after intraocular lens insertion in cataract surgery, 10 eyes achieved clearance, while three required endothelial keratoplasty later to obtain clearance.34 A 2018 retrospective chart review of 17 eyes (from 13 patients) with FECD who underwent a central 4-mm DWEK at the Massachusetts Eye and Ear Infirmary was the most extensive case series of its time.31 In this study, 14 eyes achieved clearance after the surgery, demonstrating that DWEK can be a successful surgical technique in the management of FECD. 75% percent of the eyes that underwent a 360-degree scoring technique instead of the descemetorhexis technique failed to clear, demonstrating that surgical technique was an essential factor for success. Fourteen eyes obtained clearance with DWEK, with 13 achieving a BCVA better than 20/25; the 14th eye's vision was limited by amblyopia.

Dorsey, Harold Using prior studies as inspiration, usage of Rho-associated protein kinase inhibitors (ROCKi) to enhance the outcomes of DSO was first described in 2017.35 The proposed mechanisms by which ROCKi improve outcomes is by promoting of endothelial cell proliferation, suppressing apoptosis, and increasing intercellular adhesion.36 A 2018 prospective non-placebo-controlled clinical trial involving 18 eyes (from 18 patients) undergoing DSO with or without ripasudil four times a day for two months after surgery demonstrated quicker recovery of vision in the ROCK inhibitor group (4.6 vs 6.5 weeks).37 A 2021 Mass Eye and Ear pilot study of 20 eyes (10 patients) comparing outcomes between each individual's eyes: one eye underwent DSO/PCIOL and was started on netarsudil right after surgery, while the other eye underwent DSO/PCIOL with netarsudil administration delayed at least two weeks after clearance was obtained in the first eye, and only if corneal edema was still present. The immediate netarsudil group (4.6 ± 1.7 weeks) outperformed the delayed netarsudil group (8 ± 1.9 weeks) (P < 0.01).38 Furthermore, eyes that received immediate netarsudil therapy demonstrated significantly greater endothelial cell counts than the delayed netarsudil therapy group.38 Impressively, the corneal clearance rate in this study was 100%.

Methods We used Google search to identify peer-reviewed case series, cohort studies, and/or clinical trials that track outcomes of DSO/DWEK. To be included, cases in the studies must have involved intentional removal of the central Descemet's membrane without endothelial transplantation during the same procedure to treat FECD in adults aged 18 or older. Studies that involved DSO/DWEK procedures done alone as well as those done concurrently with cataract surgery were included in our review. The use of adjuvant Rho kinase inhibitors was allowed in this literature review. Exclusion criteria included cases of endothelial failure due to a cause other than FECD, cases in which dislocation of the Descemet's layer and endothelium was not intentional, and studies with fewer than five cases. There were two studies that used the same cohort of patients; therefore, only one was included to prevent overrepresentation of the same cases.

Results A total of 14 studies were included in our literature review (Table 1). There was one retrospective cohort study, two prospective clinical trials, and eleven case series (retrospective and prospective). These studies represented a total of 278 eyes of 214 patients. Thirteen studies demonstrated that DSO/DWEK without tissue transplantation achieved corneal clearance in a majority of cases, while twelve demonstrated corneal clearance in greater? than 75% of cases. Of the eleven studies that tracked central corneal thickness (CCT), all showed a decrease in average CCT during the post-op follow-up period. Many studies had difficulty providing central endothelial cell counts (CECC) before the procedure in their patients (due to the underlying pathology). Of these eleven studies, eight reported average CECC after DSO/DWEK. Of the three studies that provided CECC before surgery, two demonstrated an increase after DSO/DWEK, and one maintained stability. Of the studies, seven used ROCKi in at least some of their patients; use cases ranged from "savior" therapies for persistent or recurrent corneal edema after DWEK/DSO to adjuvant therapy immediately postoperatively. The three studies that compared a group using ROCKi with another group that did not use ROCKi showed a decrease in time to corneal clearing in the ROCKi group. The largest of these studies, a prospective trial of DSO/DWEK with adjuvant ROCKi therapy compared to a retrospective group without ROCKi therapy, demonstrated 100% corneal clearance in both groups; however, the ROCKi group achieved statistically significant shorter time to clearance (4.5 weeks vs 18.6 weeks, P < 0.001). The ROCKi group also demonstrated statistically significant improved outcomes in visual acuity (−0.015 ± 0.04 vs 0.169 ± 0.17, P< 0.001), pachymetry (520 ± 54 vs 587 ± 51, P<0.001), and CECC (725 ± 310 vs 430 ± 258, P< 0.001) at 6 months.39

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Discussion With proper patient selection and good surgical technique, DSO/DWEK has been demonstrated to be a reasonable treatment for endothelial dysfunction in FECD. Although the corneal endothelium has been traditionally thought to be a poorly regenerative layer of tissue in vivo, its three forms of regeneration endothelial cell proliferation (to a lesser degree), cell migration, and enlargement - can play a role in the treatment of corneal endothelial degeneration. DSO/DWEK is an example of a surgical technique that can leverage the cornea's regenerative capacity as a viable therapy for FECD. This process can be further optimized with ROCKi, which are thought to enhance corneal endothelial migration and proliferation, thereby providing improved anatomical and, ultimately, visual outcomes.40 The last similar review of DSO/DWEK studies was in 2022 and had eleven studies, with only eight having more than 5 cases.41 Given that DSO/DWEK is a relatively new procedure and will likely take time to become widely used for treating FECD, this study has limitations. Most apparent is the heterogeneity of surgical and medical techniques, as well as the data/metrics collected and presented in these papers. This limits our ability to compare the results and/or outcomes between the different papers. The sizes of most of the included studies are quite small, and larger studies tracking outcomes in FECD patients who undergo DSO/DWEK will be helpful. There is also a need for further investigation comparing DSO/DWEK to endothelial keratoplasties such as DSEK and DMEK. The NIH DETECT II randomized controlled clinical trial comparing DMEK to DSO is underway and will help clarify the overlapping roles of DSO/DWEK in the treatment of FECD.42 Another limitation of this study is that a few research groups are represented multiple times in the literature review. The same patients could be represented multiple times in these cohorts, which will over-represent their outcomes in this paper. Lastly, there is a dominance of case series in the literature over prospective clinical trials, which makes it difficult to conclude that DSO/DWEK +/- ROCKi use causes corneal clearance or improvement in visual outcomes, rather than merely reflecting an association. This review demonstrates the remarkable transformation in the management of FECD over the past 25 years, from more invasive procedures, such as total corneal transplants, to tissue-sparing, endotheliumfocused techniques that do not require donor tissue. This emphasizes our transition towards a regenerative approach in managing this devastating disease, which can provide good visual outcomes while greatly decreasing the risks associated with classic corneal surgeries. DSO/DWEK is a more conservative approach to FECD management, which not only mitigates many of the risks associated with PKP, such as hypotony and endophthalmitis, but also those associated with corneal transplantation in general, such as graft failure and rejection. This particularly changes the post-operative management of FECD patients, limiting overall procedure-related morbidity and long-term topical corticosteroid usage. Furthermore, with improvements to patient selection and surgical technique over time, DSO/DWEK has demonstrated the ability to provide excellent visual outcomes despite its lower risks. DSO/DWEK, along with adjuvant ROCKi, is a unique approach to treating a form of corneal endothelial degeneration by optimizing the endothelial regenerative properties.

Dorsey, Harold

References 1.

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Aiello F, Gallo Afflitto G, Ceccarelli F, Cesareo M, Nucci C. Global Prevalence of Fuchs Endothelial Corneal Dystrophy (FECD) in Adult Population: A Systematic Review and Meta-Analysis. J Ophthalmol. 2022;2022:3091695. doi:10.1155/2022/3091695

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Moshirfar M, Ding Y, Shah TJ. A Historical Perspective on Treatment of Fuchs’ Endothelial Dystrophy: We have Come a Long Way. J Ophthalmic Vis Res. 2018;13(3):339-343. doi:10.4103/jovr.jovr_94_18

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Melles GRJ, Wijdh RHJ, Nieuwendaal CP. A technique to excise the descemet membrane from a recipient cornea (descemetorhexis). Cornea. 2004;23(3):286-288. doi:10.1097/00003226-200404000-00011

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Melles GRJ, Ong TS, Ververs B, van der Wees J. Descemet membrane endothelial keratoplasty (DMEK). Cornea. 2006;25(8):987-990. doi:10.1097/01.ico.0000248385.16896.34

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Park CY, Lee JK, Gore PK, Lim CY, Chuck RS. Keratoplasty in the United States: A 10-Year Review from 2005 through 2014. Ophthalmology. 2015;122(12):2432-2442. doi:10.1016/j.ophtha.2015.08.017

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Hakim FE, Nagra AK, Dhaliwal DK. Descemet Stripping Only: Long-term Outcomes. Cornea. 2024;43(8):994-998. doi:10.1097/ICO.0000000000003421

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Anatomy of the eye and orbit. doi:10.1016/B978-0-7020-5554-6.00001-0

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Overview of the Cornea: Structure, Function, and Development. In: Progress in Molecular Biology and Translational Science. Vol 134. Academic Press; 2015:7-23. doi:10.1016/bs.pmbts.2015.04.001

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Bonanno JA. “Molecular Mechanisms Underlying the Corneal Endothelial Pump.” Exp Eye Res. 2012;95(1):2-7. doi:10.1016/j.exer.2011.06.004

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Mootha VV, Hussain I, Cunnusamy K, et al. TCF4 Triplet Repeat Expansion and Nuclear RNA Foci in Fuchs’ Endothelial Corneal Dystrophy. Invest Ophthalmol Vis Sci. 2015;56(3):2003-2011. doi:10.1167/iovs.14-16222

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Jun AS, Meng H, Ramanan N, et al. An alpha 2 collagen VIII transgenic knock-in mouse model of Fuchs endothelial corneal dystrophy shows early endothelial cell unfolded protein response and apoptosis. Hum Mol Genet. 2012;21(2):384-393. doi:10.1093/hmg/ddr473

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Riazuddin SA, Zaghloul NA, Al-Saif A, et al. Missense mutations in TCF8 cause late-onset Fuchs corneal dystrophy and interact with FCD4 on chromosome 9p. Am J Hum Genet. 2010;86(1):45-53. doi:10.1016/j.ajhg.2009.12.001

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Ashraf S, Tone SO, Zhu S, et al. Transcriptome analyses of human corneal endothelial cell lines derived from patients with Fuchs endothelial corneal dystrophy. Sci Rep. 2025;15(1):42140. doi:10.1038/s41598-025-26025-w

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McLaren JW, Bachman LA, Kane KM, Patel SV. Objective Assessment of the Corneal Endothelium in Fuchs’ Endothelial Dystrophy. Invest Ophthalmol Vis Sci. 2014;55(2):1184-1190. doi:10.1167/iovs.13-13041

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Méthot S, Proulx S, Brunette I, Rochette PJ. The Presence of Guttae in Fuchs Endothelial Corneal Dystrophy Explants Correlates With Cellular Markers of Disease Progression. Invest Ophthalmol Vis Sci. 2023;64(5):13. doi:10.1167/iovs.64.5.13

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Matsubara M, Tanishima T. Wound-healing of corneal endothelium in monkey: an autoradiographic study. Jpn J Ophthalmol. 1983;27(3):444-450.

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Honda H, Ogita Y, Higuchi S, Kani K. Cell movements in a living mammalian tissue: Long-term observation of individual cells in wounded corneal endothelia of cats. J Morphol. 1982;174(1):25-39. doi:10.1002/jmor.1051740104

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Joyce NC, Harris DL, Zieske JD. Mitotic inhibition of corneal endothelium in neonatal rats. Invest Ophthalmol Vis Sci. 1998;39(13):2572-2583.

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Joyce NC, Harris DL, Mello DM. Mechanisms of mitotic inhibition in corneal endothelium: contact inhibition and TGFbeta2. Invest Ophthalmol Vis Sci. 2002;43(7):2152-2159.

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Joyce NC. Proliferative capacity of corneal endothelial cells. Exp Eye Res. 2012;95(1):16-23. doi:10.1016/j.exer.2011.08.014

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Kim TY, Kim WI, Smith RE, Kay ED. Role of p27(Kip1) in cAMP- and TGF-beta2-mediated antiproliferation in rabbit corneal endothelial cells. Invest Ophthalmol Vis Sci. 2001;42(13):3142-3149.

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Joyce NC, Zieske JD. Transforming growth factor-beta receptor expression in human cornea. Invest Ophthalmol Vis Sci. 1997;38(10):1922-1928.

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Hiscott P, Seitz B, Schlötzer-Schrehardt U, Naumann GOH. Immunolocalisation of thrombospondin 1 in human, bovine and rabbit cornea. Cell Tissue Res. 1997;289(2):307-310. doi:10.1007/s004410050877

31.

Davies E, Jurkunas U, Pineda RI. Predictive Factors for Corneal Clearance After Descemetorhexis Without Endothelial Keratoplasty. Cornea. 2018;37(2):137. doi:10.1097/ICO.0000000000001427

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Bleyen I, Saelens IEY, Dooren BTH van, Rij G van. Spontaneous Corneal Clearing after Descemet’s Stripping. Ophthalmology. 2013;120(1):215. doi:10.1016/j.ophtha.2012.08.037

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Iovieno A, Neri A, Soldani AM, Adani C, Fontana L. Descemetorhexis Without Graft Placement for the Treatment of Fuchs Endothelial Dystrophy: Preliminary Results and Review of the Literature. Cornea. 2017;36(6):637. doi:10.1097/ICO.0000000000001202

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Borkar DS, Veldman P, Colby KA. Treatment of Fuchs Endothelial Dystrophy by Descemet Stripping Without Endothelial Keratoplasty. Cornea. 2016;35(10):1267. doi:10.1097/ICO.0000000000000915

35.

Moloney G, Petsoglou C, Ball M, et al. Descemetorhexis Without Grafting for Fuchs Endothelial Dystrophy— Supplementation With Topical Ripasudil. Cornea. 2017;36(6):642. doi:10.1097/ICO.0000000000001209

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Syed ZA, Rapuano CJ. Rho kinase (ROCK) inhibitors in the management of corneal endothelial disease. Curr Opin Ophthalmol. 2021;32(3):268-274. doi:10.1097/ICU.0000000000000748

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Macsai MS, Shiloach M. Use of Topical Rho Kinase Inhibitors in the Treatment of Fuchs Dystrophy After Descemet Stripping Only. Cornea. 2019;38(5):529. doi:10.1097/ICO.0000000000001883

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Davies E, Jurkunas U, Pineda RI. Pilot Study of Corneal Clearance With the Use of a Rho-Kinase Inhibitor After Descemetorhexis Without Endothelial Keratoplasty for Fuchs Endothelial Corneal Dystrophy. Cornea. 2021;40(7):899. doi:10.1097/ICO.0000000000002691

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Bal S, Pineda R, Davies E. Prospective Assessment of Adjuvant Netarsudil Use in Patients Undergoing Descemet Stripping Only. Cornea. 2025;44(3):286. doi:10.1097/ICO.0000000000003578

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Kinoshita S, Colby KA, Kruse FE. A Close Look at the Clinical Efficacy of Rho-Associated Protein Kinase Inhibitor Eye Drops for Fuchs Endothelial Corneal Dystrophy. Cornea. 2021;40(10):1225. doi:10.1097/ICO.0000000000002642

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Franceschino A, Dutheil F, Pereira B, Watson SL, Chiambaretta F, Navel V. Descemetorhexis Without Endothelial Keratoplasty in Fuchs Endothelial Corneal Dystrophy: A Systematic Review and Meta-Analysis. Cornea. 2022;41(7):815. doi:10.1097/ICO.0000000000002855

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Lin CC, Chamberlain W, Benetz BA, et al. Descemet Endothelial Thickness Comparison Trial II (DETECT II): multicentre, outcome assessor-masked, placebo-controlled trial comparing Descemet membrane endothelial keratoplasty (DMEK) to Descemet stripping only (DSO) with adjunctive ripasudil for Fuchs dystrophy. BMJ Open Ophthalmol. 2024;9(1):e001725. doi:10.1136/bmjophth-2024-001725

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Table DSO/DWEK paper Study

Desig n

# of eyes | patien ts

Mean Age in Years

Sex

DWEK procedur e

P C I O L ?

RO CKi use

Cor nea s ach ievi ng cle ara nce

Tim e to cle ara nce

Me an VA pre -op

Me an VA po stop

Vieira et al 2023

Retros pectiv e case series

22 | 15

68.3 ± 9.1

73.3 %F

4 mm descemet orhexis

Y e s , A ll

No

20 (90. 9%)

3.2 ± 1.1 mo

0.4 8± 0.2 4

log MA R 0.1 3± 0.1 0P < 0.0 01

1

M ea n C C T pr eop (μ m) 53 6 ± 34 μ m [4 70 ; 59 5]

Me an CC T pos t-op (μm )

525 ± 38 μm [47 3; 583 ]P = 0.0 08

Mea n cen tral EC C preop (cell s/m m2) 6 eye s (27. 3%) with cou ntab le cent ral cells 113 8± 190 cells /mm

Mea n cen tral EC C pos t-op (cell s/m m2) 20 eye s (100 %) with cou ntab le cent ral cells 139 3± 450 cells /mm

2

2

Bleyen et al 2013

Prosp ective case series (obser vation al)

8|8

N/A

N/A

N/A

Y e s , A ll

No

1/8 (12. 5%)

N/A

N/A

N/ A

N/ A

N/A

N/A

N/A

Iovien o et al 2017

Prosp ective case series

5|5

69.8 ± 8.6

80% F

4 mm descemet orhexis

Y e s , 3 / 5

No

4/5 80 %

N/A

N/A

N/ A

59 6. 4

551 .8

N/A

Borkar et al 2016

Retros pectiv e case series

13 | 11

64.8

63.6 %F

4 mm descemet orhexis

No

10/ 13 76. 9%

N/A

N/A

N/ A

60 8. 7

567 .4

N/A

Davies et al 2018

Retros pectiv e chart series

17 | 13

N/A

N/A

4 4mm scoring (360)

Y e s , A ll Y e s , 1 6 / 1 7

100 0 (1/5 did not hav ea reco rdab le EC C) 693. 2

No

14/ 17 82. 4%

3.1 4 mo nth s± 1.7

N/A

N/ A

N/ A

N/A

N/A

Avera ge CCT and CECC

3 4mm scoring (2 clock hours) + Descemet orhexis

N/A

Dorsey, Harold were stratifi ed by time to cleara nce Molon ey et al 2017

Macsa i et al 2019

10 4mm descemet orhexis Prosp ective, interve ntional case series

12 | 11

N/A

N/A

≤ 4 mm descemet orhexis

N o

Yes , 10/ 12

9/1 2 75 %

3.4 mo nth s

Prosp ective, non– placeb ocontrol led clinical trial

18 | 18

73 women, 72 men

88.9 %F

Descemet orhexis, size unknown

Y e s , S o m e

Yes , 8/1 0

18/ 18 100 %

4.6 RO CKi gro up

0.2 6 (ran ged fro m 0.0 to 0.6)

6.5 con trol gro up, P< 0.0 1

0.1 6 (ra ng ed fro m 0.0 to 0.5 ) 10/ 10 20/ 40 or bet ter no roc ki (9 by 2 mo ,1 by 6 mo )

61 4. 9

576 .3

68 6 no R O C Ki

587 no RO CKi

70 1 Ro cki R O C Ki

N/A Onl y one of 12 was reco rded at 378 N/A

765. 6

736 no RO CKi 108 6 RO CKi

584 RO CKi

8/8 20/ 40 or bet ter roc ki 2 mo Davies et al 2021

Prosp ective case series (pilot study)

20 | 10

72

90% F

Scoring 1 to 2 clock hours followed by 4 mm descemet orhexis

Y e s , A ll

Yes , 10/ 20 19/ 20 afte r wee k2 as sav e

20/ 20 (00 %

4.6 ± 1.7 wee ks RO CKi im me diat e 8± 1.9 wee ks obs erv atio n gro

N/A

N/ A

59 5. 9 ± 27 .1 Ro cki im m ed iat e 58 9. 6 ± 32 .6

579 .9 RO CKi imm edia te, 576 .3 RO CKi dela yed

N/A

806. 1 RO CKi imm edei ate 524. 1 RO CKi dela yed or non e

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R O C Ki de lay ed

Huang et al 2018

Retros pectiv e cohort

12 | 12

67 ± 5.6

75% F

4 mm descemet orhexis

Y e s , A ll

Yes , 3/1 2

12/ 12 100 %

Tim e to 20/ 40 7.1 +/2.7 wee ks

20/ 40 (0.3 0 +/0.0 9)

20/ 30 +1 (0. 16 +/0.0 9)

61 3 ± 44 μ m for D W E K

N/A

N/A

N/A

Malyu gin et al 2017 Russia n transla tion not great

Retros pectiv e case series

20 | 19

Range 51-84

N/a

Descemet orhexis, size unknown

Y e s , A ll

N/a

63. 8%

N/a

0.3 2±0 .19

N/ a

58 7. 8± 44 .8 µ m

569 .27 ±63 .74 µm

629. 6±3 36.9 cells /mm

634. 00± 170. 41 cells /mm

Molon ey et al 2021

Prosp ective, interve ntional case series

23 | 23

67.32 (range 55–81, SD 8.3)

69.6 %F

4 mm descemet orhexis

N o

Yes , 23/ 23

22/ 23 95. 7%

4.1 wee ks

0.1 5 (SD 0.0 9)

−0. 00 2 (S D 0.1 3)

60 3. 5 μ m (S D 42 .8)

568 μm (SD 25. 9)

N/A

650

Rizk et al 2024

Retros pectiv e case series (longit udinal)

26 | 20

73 ± 9 years [52–90 years]

75 %F

4 mm descemet orhexis

Y e s , 2 0 / 2 6

No

22/ 26 84. 6%

N/A

0.3 ± 0.1 7 log MA R

0.0 9± 0.1 3 log MA R

58 8 ± 41 μ m

546 ± 50 μm

N/A

780 ± 257 [484 – 150 0]

Cohen et al 2025

Retros pectiv e case series

13 | 9

70 ± 6 years

69% F

4 mm descemet orhexis

Y e s , S o m e

Yes , 8/1 3

13/ 13 100 %

7.2 (2.4 ) We eks bot h gro ups

Pre ope rati ve BS CV A was 0.3 92 ± 0.2 7

0.2 25 (0. 26) Bot h gro up s Sn ell en eq

62 0 ± 10 0

560 ± 58 μm

N/A

778 ± 228

10/13 used "two flap” technique

5/1 3 sodi um chlo ride 5%

7.6 0± 2.6

0.6 6± 0.2 9

2

2

Dorsey, Harold We eks hyp erto nic sali ne 6.9 3± 2.4 wee ks Roc ki

Bal et al 2025

Prosp ective nonrando mized clinical trial

70 | 40

1Vieira et al 2023 2Bleyen et al 2013 3Iovieno et al 2017 4Borkar et al 2016 5Davies et al 2018

6Moloney et al 2017 7Macsai et al 2019 8Davies et al 2021 9Huang et al 2018

10Malyugin et al 2017 11Moloney et al 2021 12Rizk et al 2024 13Cohen et al 2025 14Bal et al 2025

Prospec tive trial 61.7 ± 7.5 (48– 73) Retrosp ective control 65.5 ± 8.4 (46– 76)

F to M% ratio Exp erim enta l 0.84 , Con trol 0.6

3.5-mm to 4-mm descemet orhexis

Y e s , S o m e

Yes 50/ 70

70/ 70 100 %

4.5 wee ks exp eri me ntal 18. 6 wee ks con trol

Log MA R (Sn elle n equ ival ent 20/ 50)

Exp eri me ntal 0.1 9± 0.1 2, Con trol 0.2 4± 0.1 1

uiv ale nt 20/ 30

0.2 34 (0. 27) Ro cki 0.2 12 (0. 27) Hy per ton ic sali ne ex per im ent al: −0. 01 5± 0.0 4, Co ntr ol: 0.1 69 ± 0.1 7

Ex pe ri m en tal 58 1 ± 41 Co ntr ol 59 9 ± 45

Exp eri me ntal: 520 ± 54,

Exp erim enta l 17.4 ± 30,

Exp erim enta l: 115 0± 273,

Con trol: 587 ± 51

Con trol 19.2 ± 31

Con trol: 843 ± 299

6 mo nths

12 mon ths

2026 Harvard Ophthalmology Residents’ Course

1.

Vieira R, Castro C, Coelho J, Mesquita Neves M, Gomes M, Oliveira L. Descemet Stripping Without Endothelial Keratoplasty in Early-Stage Central Fuchs Endothelial Dystrophy: Long-term Results. Cornea. 2023;42(8):980. doi:10.1097/ICO.0000000000003131

2.

Bleyen I, Saelens IEY, Dooren BTH van, Rij G van. Spontaneous Corneal Clearing after Descemet’s Stripping. Ophthalmology. 2013;120(1):215. doi:10.1016/j.ophtha.2012.08.037

3.

Iovieno A, Neri A, Soldani AM, Adani C, Fontana L. Descemetorhexis Without Graft Placement for the Treatment of Fuchs Endothelial Dystrophy: Preliminary Results and Review of the Literature. Cornea. 2017;36(6):637. doi:10.1097/ICO.0000000000001202

4.

Borkar DS, Veldman P, Colby KA. Treatment of Fuchs Endothelial Dystrophy by Descemet Stripping Without Endothelial Keratoplasty. Cornea. 2016;35(10):1267. doi:10.1097/ICO.0000000000000915

5.

Davies E, Jurkunas U, Pineda RI. Predictive Factors for Corneal Clearance After Descemetorhexis Without Endothelial Keratoplasty. Cornea. 2018;37(2):137. doi:10.1097/ICO.0000000000001427

6.

Moloney G, Petsoglou C, Ball M, et al. Descemetorhexis Without Grafting for Fuchs Endothelial Dystrophy—Supplementation With Topical Ripasudil. Cornea. 2017;36(6):642. doi:10.1097/ICO.0000000000001209

7.

Macsai MS, Shiloach M. Use of Topical Rho Kinase Inhibitors in the Treatment of Fuchs Dystrophy After Descemet Stripping Only. Cornea. 2019;38(5):529. doi:10.1097/ICO.0000000000001883

8.

Davies E, Jurkunas U, Pineda RI. Pilot Study of Corneal Clearance With the Use of a Rho-Kinase Inhibitor After Descemetorhexis Without Endothelial Keratoplasty for Fuchs Endothelial Corneal Dystrophy. Cornea. 2021;40(7):899. doi:10.1097/ICO.0000000000002691

9.

Huang MJ, Kane S, Dhaliwal DK. Descemetorhexis Without Endothelial Keratoplasty Versus DMEK for Treatment of Fuchs Endothelial Corneal Dystrophy. Cornea. 2018;37(12):1479. doi:10.1097/ICO.0000000000001742

10.

Malyugin BE, Izmaylova SB, Malyutina EA, Antonova OP, Gelyastanov AM. [Clinical and functional results of one-step phaco surgery and central descemetorhexis for cataract and Fuchs primary endothelial corneal dystrophy]. Vestn Oftalmol. 2017;133(6):16-22. doi:10.17116/oftalma2017133616-22

11.

Moloney G, Garcerant Congote D, Hirnschall N, et al. Descemet Stripping Only Supplemented With Topical Ripasudil for Fuchs Endothelial Dystrophy 12-Month Outcomes of the Sydney Eye Hospital Study. Cornea. 2021;40(3):320. doi:10.1097/ICO.0000000000002437

12.

Rizk M, Dubois M, Elahi S, et al. Long-Term Follow-Up of Descemet Stripping Only: Data Up to 7 Years Postoperatively. Cornea. 2024;43(10):1245. doi:10.1097/ICO.0000000000003449

13.

Cohen E, Din N, Aldrees S, et al. Descemet Stripping Only for Symptomatic Fuchs Endothelial Dystrophy-A Retrospective Case Series Comparing ROCK-I vs. Hypertonic Sodium Chloride for Post-Surgical Adjuvant Therapy. J Clin Med. 2025;14(5):1512. doi:10.3390/jcm14051512

14.

Bal S, Pineda R, Davies E. Prospective Assessment of Adjuvant Netarsudil Use in Patients Undergoing Descemet Stripping Only. Cornea. 2025;44(3):286. doi:10.1097/ICO.0000000000003578

Griswold, Andrew

Gene Therapy-Associated Uveitis Andrew R. Griswold, MD PhD; and K. Matthew McKay, MD

Abstract Gene therapy represents a paradigm-shifting approach to the management of retinal diseases, offering the potential for durable benefit in both rare inherited disorders and common acquired conditions. However, ocular inflammation remains a potential barrier to successful outcomes. The recently recognized complication, termed gene therapy–associated uveitis (GTAU), encompasses a spectrum of clinical presentations ranging from mild anterior chamber inflammation to irreversible chorioretinal atrophy. Current estimates suggest that GTAU affects more than 20% of patients following ocular gene therapy. As gene therapy expands beyond clinical trials and targets an increasing array of ocular disorders, timely recognition and effective management of GTAU will be critical for preserving vision and optimizing therapeutic benefit. In this review, we summarize the clinical features, proposed risk factors, and evidence-based treatment strategies for GTAU, aiming to equip ophthalmologists with practical guidance for addressing this novel challenge in the era of genetic therapeutics.

Introduction Gene therapy is an emerging technology that has revolutionized the management of inherited retinal diseases (IRDs), offering the potential for visual restoration or preservation in previously untreatable conditions.1,2 The concept of gene therapy originated in the 20th century with the belief that local transgene expression could be curative for loss-of-function Mendelian disorders.3,4 Decades of advances in molecular biology and vector engineering have led to the development of effective gene delivery systems. Throughout this time, the eye has been considered a prime organ for clinical application due to its direct accessibility, local compartmentalization, and relative immune privilege.5,6 In 2017, the United States Food and Drug Administration (FDA) approved the first ocular gene therapy, voretigene neparvovec (Luxturna, Spark Therapeutics Inc., Philadelphia, PA, USA), for biallelic RPE65-associated Leber congenital amaurosis, marking a major milestone and validating the clinical potential of gene therapy.4,7 Subsequent clinical trials have targeted a wide range of retinal dystrophies and even investigational studies for common retinal diseases such as age-related macular degeneration and diabetic retinopathy.8,9 Despite promising results in some early ocular gene therapy trials, treatment-limiting adverse ocular effects remain common. Gene therapy-associated uveitis (GTAU) can cause irreversible retinal destruction, vision loss, and limit transgene expression.10,11 The incidence of GTAU is estimated to be approximately 21 to 34%.12,13 However, there is considerable variability among trials, with reported GTAU rates ranging from 0% up to ~75% of participants.14–17 This review integrates translational studies to highlight our current understanding of GTAU, including proposed biologic mechanisms, clinical risk factors, and potential remedies.

Identification of Gene Therapy-Associated Uveitis Currently, there is no standardized regime for monitoring post gene-therapy inflammation. Patients are typically examined on postoperative day one, week one, and month one consistent with typical surgical protocol; however, considerable practice variability exists.10 Features of GTAU can be seen weeks to months after treatment, highlighting the need for ongoing surveillance.14,19–23 A combination of careful clinical examination and multimodal imaging is likely to prove crucial for prompt and accurate identification. GTAU can affect any compartment of the eye.10 Reported clinical findings include: keratic precipitates (KP), anterior chamber (AC) cell and flare, posterior-synechiae, vitreous cell and haze, vitreous snowballs, retinal vasculitis, optic disc edema, macular edema, retinitis, choroiditis and chorioretinal atrophy (CRA). The clinical presentation of GTAU seems to depend on the delivery method and space where viral particles are concentrated.

2026 Harvard Ophthalmology Residents’ Course

Multimodal ocular imaging is useful for further characterization of GTAU. Optical coherence tomography (OCT) can demonstrate retinal edema, cellular infiltration, ellipsoid zone disruption and hyper-reflective spots;18 whereas fluorescein angiography (FA) can reveal retinal vascular leakage, optic disc hyperfluorescence, and macular leakage. Fundus autofluorescence is useful for identifying hypoautofluorescence characteristic of CRA.

Vector Selection and Associated GTAU Risk Adeno-associated virus (AAV), the most utilized vector for ocular gene therapy, is formed of an icosahedral protein shell from three capsid proteins, enclosing a single-stranded DNA (ssDNA) genome.24 AAV is a replication-defective virus, which can facilitate sustained transgene expression in quiescent cells, such as the retinal pigment epithelium (RPE).25 Cellular AAV infection is a complex interplay between the viral capsule and host receptors.26 Briefly, AAV engages with low-affinity interactions to cell surface glycans, then binds with high-affinity to serotype-specific markers, and subsequently is internalized via endocytosis.27 Many viral particles are degraded by the ubiquitin-proteosome system; however, those that escape can be transported to the nucleus via phospholipase A2 domain exposure and activation. There, the viral ssDNA genome is released and undergoes DNA synthesis and concatemerization to form double stranded episomal DNA distinct from the host genome. Promoter selectivity determines whether transgene expression is ubiquitous or cell-specific (often photoreceptor or RPE). Multiple AAV serotypes enable tissue-specific transduction.26,28 Approximately 30-60% of the general population harbor pre-existing antiAAV antibodies,29 which may neutralize AAV-particles and reduce transfection efficiency.30 Limitations of AAV include its modest cargo capacity at 4.7 kb of DNA and the complexity of medical-grade AAV production.31 Nevertheless, AAV remains the preferred delivery system for genetic material compared to lentivirus (limited by the risk of insertional mutagenesis and oncogenesis) and adenovirus (limited by fervent immunogenicity).26 AAV vector dose appears to be a strong predictor of GTAU severity. Clinical trials have administered AAV vectors doses from ~1 x 108 to ~3 x 1012 viral genomes (vg)/eye.11,32,33 In an early dose-escalation study for RPE65-associated LCA, there was a stark difference in adverse effects between doses, highlighting the narrow therapeutic window of AAV vectors.11 Of patients receiving the higher dose of vector (1 x 1012 vg/eye), 37% developed intraocular inflammation (optic disc swelling, vasculitis, vitritis and/or anterior uveitis), whereas none of the patients receiving the lower dose of vector (1 x 1011 vg/eye) demonstrated signs of inflammation. Viral genome titers are challenging to measure accurately. Manufactured batches of AAV vectors are commonly quantified by quantitative polymerase chain reaction which can produce variable concentration estimates.34,35 The likelihood of GTAU appears to significantly increase when doses exceed ~5 x 1010 to 1 x 1011 vg/eye.10 Retrospective analysis of other AAV-related factors has demonstrated variable associations with GTAU. For example, engineered AAV capsids are associated with higher incidence of anterior uveitis than natural AAV capsids (54% versus 15%).12 Conversely, the type of AAV promoter (retina-specific versus ubiquitous) and transgene product location (intracellular versus extracellular) do not significantly affect the rates of uveitis in gene-therapy trials.12 Efforts to modify AAV-genomes to optimize transgene expression and immune evasion are ongoing.

Route of Administration and Associated GTAU Risks There are three primary routes of ocular gene therapy administration – intravitreal, subretinal, and suprachoroidal – each with unique advantages and disadvantages. Intravitreal delivery involves direct injection of vector into the vitreous cavity through the pars plana. This method is simple, minimally invasive, and relatively safe, avoiding surgical risks of vitrectomy. Intravitreal delivery better targets inner retinal cells, including ganglion cells, bipolar cells, and Müller glia. However, transduction of outer retinal cells is restricted by the internal limiting membrane (ILM) with current vectors, and there is risk of off-target transduction of anterior segment structures.36,37 Intravitreal delivery is

Griswold, Andrew associated with higher rates of GTAU, perhaps related to larger required vector doses to achieve therapeutic concentrations and a stronger neutralizing antibody response directed against the viral capsid.12 Administration of at least 1 x 1010 vg/eye is common for intravitreal gene therapy trials.38–40 The doseescalation REVEAL study (NCT02064569) for ledanogene nolparvovec in LHON tested four vector concentrations: 9 x 109, 3 x 1010, 9 x 1010, and 1.8 x 1011 vg/eye.39 The study found ocular inflammation in one patient in the lowest vector group and in all patients treated with higher doses. Subsequent trials of ledanogene nolparvovec, with 174 patients treated at 9 x 109 vg/eye, found an intraocular inflammation rate of 75%, compared to 10% of sham-injected eyes.40 Frequent observation of anterior and intermediate ocular inflammation following intravitreal gene therapy administration reinforces the theory that location and concentration are primary driving factors of GTAU. Subretinal delivery places the vector in direct contact with outer retinal cells. Of note, this is the FDAapproved method of administration for voretigene neparvovec.7 Subretinal delivery by pars plana vitrectomy (PPV) and injection of the vector into the subretinal space allows for maximal transduction of the retinal pigment epithelium (RPE) and photoreceptors, lower required viral vector load, and direct delivery to an immune-privileged location. Administration by this method is technically complex, and potential complications include long-term macular detachment and iatrogenic damage.41 A commercial system to access the subretinal space externally via the choroid is under development to alleviate this challenge.42,43 Another constraint is that transduction and transgene expression appear to be limited to the bleb area. Subretinal gene vector administration is more commonly associated with choroidal thickening, chorioretinitis and CRA.20,44,45 As with other forms of GTAU, this appears to be dose-dependent. Nonhuman primate studies have shown that CRA occurs twice as frequently, and progresses more rapidly, in animals treated with 1 x 1012 compared to 1 x 1011 vg/eye.46 The immune response is strongest at the subretinal space within and around the bleb, with localized immune infiltration centered at these sites of maximal vector concentration. Efforts to increase AAV delivery by dividing particles between multiple blebs have had little effect on overall intraocular inflammation.47–49 Another source of ocular inflammation from subretinal delivery is vector reflux through the retinotomy or areas of retinal degeneration.50 Release of viral particles into the vitreous cavity is thought to be a primary driver of anterior and intermediate uveitis following subretinal treatment. Indeed, complications with bleb induction are associated with higher rates of vitritis.51 Extended vitreous washout and shaving of the cortical vitreous during surgery have been proposed to reduce vector reflux and mitigate GTAU risk.50 A meta-analysis compared the rates of GTAU between clinical trials using intravitreal and subretinal vector delivery. It found a higher incidence of both anterior uveitis as well as intermediate/posterior uveitis with intravitreal relative to subretinal administration (43% versus 10%; and 40% versus 6% respectively).12 While there are not direct comparisons of CRA rates, this complication is more often described in trials with subretinal gene administration.10 Advances in gene-delivery technology and surgical techniques will continue to shape the risk benefit portfolio for ocular gene therapy administration. Suprachoroidal gene therapy is accomplished by injection of vector into the potential space between sclera and choroid with a microneedle. This procedure can be performed in a specialized outpatient setting without the need for intraocular surgery. It has the potential to treat a large area of RPE. Disadvantages of this route include the increased likelihood for systemic immune response given the highly vascularized space,52 low transduction efficacy to the neurosensory retina, and risk of choroidal detachment. Suprachoroidal delivery has been used in few dose-escalation clinical trials, so its associated rate, spectrum, and dosedependency of GTAU remains uncertain. Early data suggests that episcleritis is the most common presentation of ocular inflammation.10

Vector Immunogenicity and Host Immune Response While AAV vectors have relatively low immunogenicity, the host immune system still harnesses a targeted response to vector components and transgene products, providing a molecular basis for GTAU. The innate immune system recognizes pathogen-associated molecular patterns through an arsenal of genetically encoded pattern-recognition receptors (PRRs) to initiate immune responses. Toll-like receptors (TLRs) are a class of PRRs expressed on the cell surface or within endosomal compartments in both immune and non-

2026 Harvard Ophthalmology Residents’ Course immune cells.53 TLR2 and TLR9 are recognized components of the pro-inflammatory pathway in GTAU.54 Capsid proteins of extracellular viral particles are detected by TLR2 and unmethylated CpG motifs of viral ssDNA are recognized by TLR9.55,56 Activation of TLR2/TLR9 initiates the MyD88 signaling pathway, with subsequent MAPK kinase activation and NF-κB transcription. Together this promotes production of proinflammatory cytokines, including interleukin (IL) IL-1, IL-6, IL-12, and tumor necrosis factor (TNF), TNFα.57 Transgene products may also be detected by intracellular cyclic guanosine monophosphate-adenosine monophosphate synthase (cGAS), which activates stimulator of interferon genes (STING).58 The cGASSTING pathway recognizes cytoplasmic dsDNA in a sequence-independent manner, triggering the expression of type-I interferons. Indeed, upregulation of both cGAS-STING and TLR2/TLR9 have been identified in murine models of GTAU.59 Evidence suggests that AAV vectors also trigger a strong cell-mediated immune response with activation of Th1 cells. Multiple murine models have demonstrated accumulation of CD45+ immune cells in the retina following subretinal and intravitreal administration of AAV vectors.60,61 Tummala and colleagues investigated the immune response to intravitreal injections of recombinant AAV vector encoding for green fluorescent protein in mice.60 Vitritis occurred in all AAV-treated eyes, peaking at seven days and becoming subclinical within one month. Nevertheless, flow cytometry revealed persistent immune infiltrate with distinct populations over time – early macrophages and neutrophils (day one); intermediate T cells, macrophages and natural killer cells (day seven); and late CD8+ T cells and microglia (day twenty-nine). Chandler and colleagues looked at the murine response to subretinal delivery of AAV-green fluorescent protein.61 Here, the CD45+ response peaked 14-28 days after subretinal injection. The upregulated populations included macrophages, natural killer cells, CD4 and CD8 T cells, with minimal change in the resident microglial population. They demonstrated a prolonged inflammatory course with immune infiltration lasting beyond 1 month. Large-animal models (including non-human primates) treated with ocular AAV vectors similarly demonstrate a phenomenon of cell-mediated immune response, including increased levels of type 1– associated cytokines (IFN-γ, TNF-α, and CXCL10) and activation of retinal antigen-presenting cells.44,62,63 Systemic immune responses can occur in ocular gene therapy.12 In a phase I/IIa trial of AAV8-RS1 gene therapy in patients with X-linked retinoschisis, analysis of serum demonstrated peripheral immune activation with increased activated lymphocytes, macrophages, and proinflammatory cytokines such as IFN-γ and granzyme B.64 Likewise, intraocular AAV administration in nonhuman primates results in a dosedependent increase in serum neutralizing antibodies.65 AAV particles have even been found in draining lymphoid following ocular injection of nonhuman primates.46 Vector DNA sequences have been detected in postoperative patient tears and peripheral blood mononuclear cells.15 There is emerging data to support a posterior ocular lymphatic drainage system which facilitates recruitment of T cells to the retina.66 The specific retinal cell type that initiates GTAU remains unclear; however, microglia are at least partially responsible for early leukocyte infiltration.59

Prophylactic Immunomodulation for GTAU Inflammatory complications of gene therapy in pre-clinical and clinical studies highlight the need for appropriate immunomodulation to control GTAU. Early trials often took a conservative approach towards management of ocular inflammation. Patients received postoperative steroid drops for a specified duration of time (typically three or more weeks).21,33,47,67 Episodes of ocular inflammation were treated with a combination of topical steroid drops, local steroid depots, and/or systemic steroids according to provider preference. Reports of inflammation resolution with steroids suggested a possible role for prophylactic treatment. Indeed, one study initiated 60 mg oral prednisone beginning 2 days prior to vector administration, after remarking on the improvement in prior participants with oral steroid treatment.19 In the landmark phase III trial of voretigene neparvovec, patients assigned to the intervention group received 1 mg/kg per day oral prednisone for 7 days.7 Similarly, in a phase II trial for AAV2-REP1 in choroideremia, patients received oral prednisone, 1 mg/kg per day, for 21 days.22 Trials are now tending to favor prophylactic immunosuppression, with 39% of trials employing a prophylactic regimen.10 The efficacy of prophylactic corticosteroids is not fully understood and is challenging to study given variability between trial protocols. A recent meta-analysis of 29 studies implementing prophylactic immunomodulation sub-divided analysis by route of administration.12 For intravitreal delivery, average

Griswold, Andrew incidence of anterior uveitis was 24% vs. 43% and intermediate/posterior uveitis 15% vs. 44%, with and without immunomodulation, respectively. For subretinal administration, average incidence of anterior uveitis was 8% vs 11% and intermediate/posterior uveitis 4% vs. 8%, with and without immunomodulation, respectively. Neither of these differences were statistically significant. Analysis of 80 patients across 17 studies demonstrated a statistically significant reduction in systemic immune responses (including fever, leukocytosis) for participants treated with steroids compared to no steroids (25% vs. 42%) prior to intravitreal administration of AAV12 Together, these data tend to support prophylactic immune suppression for reducing GTAU. In accordance with this premise, GTAU is often observed after immunosuppression is withdrawn or the steroid dose falls below an adequate level, typically 15-20 mg.11,68 Prophylactic steroids do not prevent ocular inflammation in all studies. Both the phase I/II and phase II/III trial for BIIB112/AAV8-RPGR (cotoretigene toliparvovec) in X-linked RP observed >30% incidence of GTAU despite extended oral steroid courses (3-weeks and 3months in the respective trials).20,69 The best direct comparison of prophylactic steroid likely comes from the LHON literature. The REVERSE (NCT02652780), RESCUE (NCT02652767), and REFLECT (NCT03293524) trials all administered the same rAAV2/2-ND4 intravitreal vector, with REFLECT being the only trial where patients received prophylactic immunomodulation (4 weeks of oral prednisone). All three studies reported similar levels of ocular inflammation.17,40,70 Steroid-sparing agents may offer an alternative route of prophylaxis against GTAU, albeit from a paucity of data. One trial used a regime of cyclosporine, mycophenolate mofetil, and corticosteroids three weeks prior to intravitreal AAV vector in two cases of X-linked retinoschisis. These patients demonstrated dampened ocular inflammatory responses compared to patients managed with steroids alone.64 While not prophylactically administered, methotrexate has been effectively used to treat GTAU arising from intravitreal administration of rAAV2tYF-CB-hRS1 for X-linked retinoschisis.71 More evidence is needed to clarify the role for such medications in the management or prevention of GTAU.

Conclusion There has been extraordinary progress over the past decades in retinal gene therapy. A therapeutic modality once reserved for science fiction is on the precipice of revolutionizing how ophthalmologists manage blinding eye conditions both rare (IRDs) and common (age related macular degeneration, diabetic edema). Clinical trials have shown that AAV vectors can effectively express the desired transgene product without detectable oncogenesis. Yet, there is a narrow therapeutic window, often limited by ocular inflammation. Here we reviewed existing data about the clinical presentation and natural progression of GTAU. Multiple factors are likely associated with GTAU incidence including vector immunogenicity and dosing, route of administration and surgeon technique, as well as the host immune system and selection of immunomodulatory regimens. The multifactorial nature of GTAU and variability between clinical trials make it challenging to untangle how each factor affects downstream inflammatory changes. Standardized reporting for clinical gene therapy trials to include specific immunomodulatory regimens and immune outcomes will be necessary.10,12 Ultimately, appropriate recognition and management of GTAU will be paramount to the successful implantation of ocular gene therapy.

Future Perspectives While gene augmentation via AAV vector expression is currently the favored modality for gene therapy, other strategies are under development. Gene editing with CRISPR/Cas9-based systems is one such alternative. A small pioneering trial of 12 patients with CEP290 (IVS26 variant) associated LCA were treated with an AAV5 vector encoding for Cas9 and two guide RNAs. Impressively, nine subjects had meaningful visual improvement from baseline.32 Another alternative gene-therapy approach is optogenetics.72 This approach aims to express light-sensitive proteins in diseased retina thereby enabling photon sensing with residual neurons. Early clinical trials are underway with the hope that optogenetics could be a gene-agnostic approach to vision restoration. A promising case report from the Roska group showed that intravitreal administration of an AAV encoding for ChrimsonR, when coupled with special goggles, was able to restore

2026 Harvard Ophthalmology Residents’ Course some visual function in a blind patient.73 Finally, it is worth noting that cell-based therapies are a third way to sustainably generate a recombinant protein product following a single treatment. Indeed, revakinagene taroretcel-lwey, which uses encapsulated RPE cells to continuously express recombinant human ciliary neurotrophic factor, was recently FDA-approved for treatment of idiopathic macular telangiectasia type 2.74,75 The immunogenicity and host response to these emerging therapeutic strategies remains to be seen. Regardless, in a field long cast in darkness, the future for debilitating retinal disease may indeed be bright.

Griswold, Andrew

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Macular Telangiectasia Type 2: A Focused Review and Therapeutic Update Mary K. Munsell, MD; Ioanna Ploumi; and Leo A. Kim, MD, PhD

Abstract In March 2025, the United States Food and Drug Administration approved revakinagene taroretcel (formerly NT-501; ENCELTO) for macular telangiectasia type 2 (MacTel). This ciliary neurotrophic factor (CNTF) releasing implant represents a milestone in the treatment of MacTel, a degenerative retinal disease. This review will discuss the current literature on the pathophysiology and natural history of MacTel, imaging findings, potential outcome measures, and current and potential future therapeutic options, with particular attention to the underpinnings and implications of CNTF therapy. The pathogenesis of MacTel involves abnormal serine metabolism, mitochondrial dysfunction, and damage to Müller cells and photoreceptors; genetic contributions exist but their exact mechanism remains unclear. CNTF has been found to have retinal neuroprotective effects with variable functional benefit for vision. MacTel has been evaluated using multimodal imaging platforms including fluorescein angiography, optical coherence tomography (OCT), and OCT angiography. Visual deficits in MacTel are likely better reflected by perimetric methods than by visual acuity. Loss of the ellipsoid zone (EZ) on OCT has been studied as a marker for functional decline. Eyes with neovascular complications are treated with antivascular endothelial growth factor (VEGF) injections, whereas non-neovascular disease can now be treated with the CNTF-releasing implant revakinagene taroretcel. Two phase 3 trials showed significant anatomic stabilization with revakinagene taroretcel but no consistent improvement in visual function outcomes. Metabolic therapies under current investigation include serine supplementation and fenofibrate treatment.

Introduction Macular telangiectasia (MacTel) type 2 is a degenerative disease of the neurosensory retina. MacTel type 2, or idiopathic juxtafoveal telangiectasia, was first described by Gass in 1968 in contrast to Coats disease.1 It was later classified as separate from both the unilateral, congenital disease called macular telangiectasia type 1 and the rare idiopathic form referred to as type 3.2 Clinically, MacTel type 2 is typically bilateral and presents in middle age with paracentral scotomas and metamorphopsia.3 As its name suggests, MacTel was first understood as a vascular disease based on the clinical appearance of telangiectatic retinal vessels.4 However, in vitro and imaging studies have revealed the pathogenesis to be related to degeneration and loss of Müller cells with secondary loss of photoreceptors.5 On this background of neurodegenerative disease, vascular complications including characteristic capillary telangiectasias and subretinal neovascularization arise.5 Although MacTel type 2 affects up to 0.1% of the population based on the Beaver Dam Eye Study, treatment options have been extremely limited.6 In March 2025, revakinagene taroretcel (formerly NT501; ENCELTO), an implanted cell-based therapy which slowly releases ciliary neurotrophic factor (CNTF), was approved by the United States Food and Drug Administration (FDA) to treat MacTel type 2.7 In this review, we discuss the current understanding of the underlying pathogenesis of MacTel, the natural history including clinical and imaging findings, and other burgeoning and prospective therapies for this degenerative disease.

Pathophysiology

Mechanism The development and progression of MacTel are driven at least in part by altered serine metabolism leading to toxic accumulation. Serine acts as a substrate for serine palmitoyl transferase (SPT) in the synthesis of sphingolipids. Mutations in SPT subunits as well as increased utilization of non-serine

Munsell, Mary substrates lead to increased levels of deoxysphingolipid byproducts which have been found to contribute to neurotoxicity in MacTel as well as in human hereditary sensory and autonomic neuropathy (HSAN1), a neurodegenerative disease.8 Mice fed a serine-deficient diet leading to low circulating serine levels had a corresponding increase in deoxysphingolipids both in serum and within the retina and retinal pigment epithelium (RPE). These mice also had significantly decreased photopic and flicker responses on electroretinography (ERG).9 Multiple case-control studies have identified significantly lower serum levels of serine in MacTel patients than in unaffected controls;9,10 Gantner et al. also identified a more than 80% increase in serum levels of deoxysphingolipids in MacTel patients.9 The mechanism by which deoxysphingolipids induce retinal degeneration is incompletely understood, but appears to involve mitochondrial dysfunction affecting Müller cells and photoreceptors. In one transcriptome study, deoxysphingolipid accumulation was shown to activate specific arms of the unfolded protein response involved in endoplasmic reticulum stress responses, triggering inflammatory signaling pathways in retinal organoids and inducing apoptosis of Müller cells and photoreceptors. Gene expression patterns in other retinal cell types were minimally affected.11 Transgenic mouse models in which Müller cells were conditionally ablated developed a phenotype markedly resembling MacTel: apoptosis of photoreceptors as well as vasculopathy, with formation of macular macular telangiectasias, compromise of the blood-retinal barrier, and eventually intraretinal neovascularization.12 Electron microscopy of a postmortem human retina with MacTel showed mitochondrial changes – swelling, loss of cristae, and accumulation of electron-dense material – across retinal cell types not only within the disease-affected zone, but also in otherwise healthy-appearing portions of the retina.13 As in other pathologic studies, Müller cells were found to be particularly affected within the MacTel zone, with absence of normal Müller cell process encasement of Henle fibers and photoreceptor cell bodies.13,14 Within the area of Müller cell dysfunction, cone outer segments are also disorganized with prominent mitochondrial changes.13 RPE cells derived from induced pluripotent stem cells from MacTel patients have been shown to have reduced mitochondrial function even after CRISPR correction of the mutation causing decreased serine biosynthesis, suggesting one or more pathways of damage independent of serine metabolism and deoxysphingolipid accumulation.15 Parallel studies have not been performed in Müller cell and photoreceptor populations. Genetics MacTel is thought to have a significant heritable component. Families with very high incidences of MacTel have been described, but typically lack a clear inheritance pattern. One cross-sectional study assuming autosomal dominant inheritance calculated a genetic penetrance of 0.38.16 A single responsible gene has proven elusive; one screening study sequenced 27 candidate genes implicated in the pathophysiology of MacTel and similar diseases but found no variants that segregated with disease status within families of 400 MacTel patients.17 Phosphoglycerate dehydrogenase (PHGDH) mutations have been identified in 3% of patients with MacTel.18 The most common variant is associated with reduced serine synthesis and increased deoxysphingolipid accumulation in RPE cells, but 22 other rarer variants in PHDGH were also identified in a large MacTel cohort.18 Another small subset of patients with MacTel was found to have variants in serine palmitoyltransferase long chain base subunit 1 (SPTLC1), which encodes a subunit of SPT.9 Two genome-wide association studies (GWAS) of MacTel have identified eleven statistically significant loci, several of which are associated with glycine-serine metabolism.19,20 These include two variants in PHGDH and one in phosphoserine phosphatase (PSPH), both of which encode enzymes in serine biosynthesis, as well as one variant each in carbamoyl phosphate synthetase 1 (CPS1) and solute carrier family 6 member 20 (SLC6A20), which are involved in glycine metabolism. Glycine and serine are closely metabolically linked amino acids. Other loci were found within ceramide synthase 4 (CERS4), which encodes an early enzyme in ceramide synthesis upstream of sphingolipid formation, within tetratricopeptide repeat domain 39B (TTC39B), which may play a role in hepatic cholesterol metabolism, and adjacent to transmembrane protein 161B (TMEM161B), which could be involved in retinal vasculogenesis. Interestingly, transcriptome analysis within the same study showed that about half of implicated genes were more highly expressed in RPE and choroid than in the neurosensory retina. Of note, the 11 identified variants account for only 0.65% of the heritability of MacTel.19

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Though MacTel within families does not generally follow a maternal inheritance pattern, there has been speculation about a role for mitochondrial mutations in at least a portion of MacTel patients. Two patients with large-scale deletions in mitochondrial DNA have been reported with a clinical and imaging phenotype consistent with MacTel.21 MacTel has also been reported in one patient with a nuclear DNA variant in cytochrome P450 family 2 subfamily U member 1 (CYP2U1), which is expressed in mitochondria and involved in respiration.22 Ciliary neurotrophic factor The effects of ciliary neurotrophic factor (CNTF) in MacTel have taken on increasing clinical relevance in the setting of new therapeutic use of CNTF, which is reviewed below. CNTF is produced endogenously within the retina and upregulated by photostress and trauma. CNTF is expressed mainly within Müller cells and is stored in granules within cell processes throughout the retinal layers.23 More than 25 years ago, CNTF was identified as protective against photoreceptor damage in multiple animal studies modeling inherited retinal degenerations.24,25 These studies utilized both injection of exogenous CNTF and gene therapy to induce endogenous expression. Despite improved photoreceptor survival and normalized photoreceptor morphology following subretinal injection of lentiviral CNTF, however, one mouse study in a retinitis pigmentosa (RP) model found no ERG improvement.26 Interestingly, CNTF therapy normalized mitochondrial morphology in photoreceptors, but metabolomic analysis indicated higher rates of glycolysis and lower respiratory chain activity.26 It is unclear whether these metabolic alterations mediate the therapeutic effect of CNTF or represent off-target effects. Cytokine induction may be a necessary step downstream of CNTF expression: deletion of gp130, which encodes a Müller cell cytokine receptor, negated survival effects of CNTF in a mouse model of RP.27 One study focused on retinal ganglion cells suggests a candidate for one of these downstream molecules. In a mouse optic nerve crush model, CNTF gene therapy promoted retinal ganglion cell survival, but inhibition of C-C motif ligand 5 (CCL5) abrogated the neuroprotective effects of CNTF treatment, and treatment with recombinant CCL5 produced similar ganglion cell protective results.28 Early investigations showing the neuroprotective effects of CNTF did not model MacTel specifically. In transgenic mice with conditionally ablated Müller cells, intravitreal injection of recombinant CNTF 7-10 days after Müller cell ablation reduced photoreceptor apoptosis compared to untreated controls. However, CNTF therapy did not prevent breakdown of the blood-retinal barrier.12 In a mouse model resembling MacTel with subretinal neovascularization, sustained delivery of a different neurotrophic factor, neurotrophin-4 (NT4), via viral vector improved photoreceptor survival and normalized ERG.29

Diagnosis

Clinical Presentation MacTel type 2 is acquired, nearly always bilateral, and typically presents between age 40-60.2,30 Early telangiectasias are often very subtle on exam with relatively little associated exudation and retinal thickening compared to other telangiectatic diseases. Other key clinical characteristics include retinal graying, loss of central macular pigment, crystalline deposits, right-angled venules, and plaques of RPE hyperplasia typically located at the tips of dilated venules.30 Neovascularization occurs as a complication in a subset of patients. This is often referred to as subretinal neovascularization (SNV); unlike the choroidal neovascularization of age-related macular degeneration, vessels are retinal in origin but may form anastomoses with the choroidal vasculature.31 Patients with SNV or atrophy are more likely than other patients to develop the same complication in the fellow eye; up to 33% of neovascularization cases are bilateral. Even advanced MacTel changes generally affect a discrete and well-defined ovoid area, longer horizontally, within the central macula.32 Fluorescein Angiography On fluorescein angiography (FA), there is rapid staining of telangiectatic capillaries, followed by late staining of the surrounding perifoveolar retina with foveolar sparing. The late, diffuse hyperfluorescence is thought to originate from the outer retina and can precede telangiectatic changes.2 As this is less consistent with capillary leakage, some have theorized that late hyperfluorescence is a relative window

Munsell, Mary defect caused by loss of macular pigment.33 No pooling is seen to correspond with inner and outer retinal cavitations seen on OCT.30 Fundus Autofluorescence Fundus autofluorescence (FAF) uses excitation by shorter wavelength blue or green light to visualize macular pigment changes and abnormalities in lipofuscin. FAF is often abnormal in MacTel, but is nonspecific. FAF with 488 nm blue light shows perifoveal hyperautofluorescence due to loss of the central macular pigment, which typically masks lipofuscin reflectance. Distinct hyperautofluorescence is seen in areas of outer retinal atrophy and hypoautofluorescence at sites of pigment plaques due to window effect and blocking, respectively.34 Retinal cavitations on OCT also correspond to areas of hyperautofluorescence, consistent with focally decreased retinal light absorption.35 Optical Coherence Tomography The era of OCT has brought significantly increased understanding of both the mechanisms and progression of MacTel. While FA findings in MacTel would suggest that vascular leakage and retinal thickening are part of the pathogenesis, OCT in fact shows overall retinal thinning.36 Macular edema may be present in eyes with neovascularization, but cystoid macular edema is not generally seen in nonproliferative cases.37 Extension of the foveal depression temporally has been described as an early OCT sign of MacTel.33 Progressive ellipsoid zone (EZ) loss also occurs in the temporal perifoveal region.38 As disease progresses, OCT findings include outer retinal atrophy with cavitations, which can be confused with edema.30 Inner retinal cavitations also occur. These are typically oriented vertically in the central foveola, and horizontally along the slope of the fovea.40 This corresponds to the histologic position of the Müller cell cone, a cluster of cells which interface with central cones and appear to structurally support the foveola.39 Unlike macular holes, inner retinal cavitations in MacTel have overlying internal limiting membrane (ILM) and no associated traction from epiretinal gliotic tissue.40,41 However, true macular holes have also been described in patients with MacTel and present a therapeutic challenge with low rates of surgical closure.42 Intraretinal and subretinal neovascularization are associated with hyperreflectivity on OCT, which develops within or bordering areas of EZ loss, and appears to occur after neovascularization is visible on angiography.43 The MacTel Classification system was developed from a prospective natural history cohort of 1,733 participants based on multimodal imaging findings with change in BCVA from baseline as the primary outcome. OCT characteristics – presence of EZ loss, presence of hyperreflectivity – and the presence of pigmentation on exam or fundus photos are used to assign severity grades from 0 (MacTel without risk factors for progression) to 7 (neovascularization present) for eyes already diagnosed with MacTel.44 Optical Coherence Tomography Angiography OCT angiography (OCTA) represents a potential non-invasive alternative to FA for diagnosing and following MacTel and its characteristic vascular findings. Patients with early MacTel changes have significantly decreased vascular density in the deep capillary plexus (DCP) as well as telangiectatic vessels, which correspond with those seen on FA.45-47 Superficial capillary plexus changes, as well as telangiectatic, sometimes microaneurysm-like vessels in the middle retina are seen later in the disease course.45,48 On swept-source OCTA, which better visualizes deeper structures, neovascular complexes appear to originate from the outer retina and communicate with the choroidal vasculature.45,49 Retinalchoroidal anastomoses have also been described without accompanying retinal or subretinal neovascularization; an average of 55 such anastomoses were seen in 22 of 43 imaged MacTel patients.50 Confocal Reflectance Imaging Hyperreflectance of the parafoveal region on confocal imaging with blue light at a wavelength of 488 nm has been shown to correspond to areas of macular pigment loss clinically.51 This medium has been proposed as a non-invasive diagnostic tool to differentiate particularly early MacTel from other diseases. However, another small study showed no confocal blue hyperreflectance in four eyes with less severe disease in which OCTA changes were present.47 Confocal infrared reflectance imaging, in contrast,

2026 Harvard Ophthalmology Residents’ Course shows hyperreflectance that corresponds with areas of leakage on FA and hyporeflectance over pigment clumps or SNV, and thus may be useful for monitoring disease progression.51 Adaptive Optics Adaptive optics (AO) uses a wavefront sensor to detect aberrations in the eye and correct for these aberrations. When used in combination with a scanning laser ophthalmoscope (SLO), individual photoreceptors can be visualized and pathologic changes identified. AO-SLO in 13 eyes with nonproliferative MacTel showed significantly decreased cone density compared to controls within the perifovea. Dark regions on AO-SLO generally corresponded to areas of leakage on FA, but dark spots were also seen in areas that appeared normal on FA.52 Interestingly, longitudinal AO-SLO and OCT in 10 eyes with MacTel identified intact cone structures within foveal areas of EZ loss on OCT, with minimal loss of remnant cones over one year of follow-up. In four eyes, areas of cone mosaic re-emerged within spots that had been dark at baseline.53

Outcome Measures

Visual Acuity Identifying and tracking relevant outcome measures is a challenge in MacTel. Central visual acuity is relatively preserved, even in patients with advanced disease. The MacTel Natural History Observation Study found that 37.3% of patients had best-corrected visual acuity (BCVA) of 20/50 or worse, with only 3.8% at 20/200 or worse.32 BCVA decreased significantly over time, but by only 1.07 Early Treatment Diabetic Retinopathy Study (ETDRS) letters per year of follow-up.54 Visual Fields Microperimetry has been used to visualize and track scotomata associated with MacTel. These scotomata are typically temporal and very rarely exceed 40 degrees squared of visual field.55 In one cross-sectional study, retinal sensitivity was normal in patients with early disease, but a scotoma typically about 2 degrees temporal to fixation was seen in all patients with areas of pigment accumulation and SNV.56 Over a mean 55 months of follow-up, another study found that microperimetry demonstrated scotoma enlargement in 94% of 33 patients with a baseline absolute scotoma, while only 17% showed a BCVA decrease of two ETDRS lines or more. However, only 26% of 38 eyes with no baseline scotoma developed a new scotoma on microperimetry, leaving 39% of included eyes with no microperimetric disease.57 Fine matrix mapping (FMM), which uses a custom grid input to a Humphrey field analyzer to present high density stimuli over a 9x9 degree field, identified scotomata not detectable by microperimetry in one controlled study of nine patients. Unlike microperimetry and photopic FMM, FMM under dark-adapted conditions showed significant worsening over one year of follow-up.58 Microperimetry and particularly FMM are relatively time-consuming to perform and analyze; as in other forms of visual field mapping, fixation loss and testing variability introduce complication. Learning effects have been described with improvement on repeat testing.58,59 Unfortunately, Amsler grid testing has been shown to have poor sensitivity in detecting MacTel scotomata.60 Visual Function Patients in the MacTel Natural History Observation Study had significantly lower scores on the National Eye Institute Visual Functioning Questionnaire (NEI-VFQ) than normal controls across all domains (including near activities, distance activities, driving, peripheral vision, mental health) except color vision. NEI-VFQ scores were only moderately correlated with BCVA.61 Meaningfully decreased reading acuity (the print size threshold at which a patient can read an entire sentence) and reading speed have also been documented in MacTel patients, with average speed of 141 words per minute compared to 190 in controls.62 Though poorer BCVA was significantly correlated with slower reading speed, patients with normal BCVA also had decreased reading speed.62 Ellipsoid Zone Loss Imaging studies in MacTel have variably shown structure-function correlates between EZ loss on OCT and visual function, leading to the use of EZ loss as a surrogate measure of visual function in subsequent trials. In the MacTel Natural History Observation Study, the categorical presence of central EZ loss was

Munsell, Mary significantly correlated with greater BCVA loss, but EZ loss progression was not quantified.54 In a smaller cohort of 56 eyes from the same study group, ellipsoid zone (EZ) loss on OCT involved a median area of 0.59 mm2 and increased by 0.08 mm2 per year over a median 4.5 years of follow-up. Growth in EZ loss was significantly correlated with progression of both relative and absolute scotoma size by microperimetry. EZ loss was noted to correspond better spatially to areas of relative scotoma than to absolute scotoma. However, statistical analysis was performed using only the overall rate of change in EZ loss compared to the overall rate of change of relative or absolute scotoma; no formalized quantitative comparison of expansion patterns was undertaken. Also of note, there was no significant correlation between growth in EZ loss and decrease in BCVA.38 In another recent study outside the MacTel Natural History database, area of EZ loss progressed by a median of 0.08 mm2 per year. EZ loss paired with loss of overlying retinal architecture was associated with significantly higher rates of progression.63 Of note, EZ loss does not seem to necessarily correspond in MacTel to complete absence of photoreceptors, nor to permanent damage: longitudinal AO-SLO and OCT has shown remnant cone structures in areas of EZ loss.53 In six total eyes across two similar studies, EZ reflectivity recovered during follow-up in areas of previous loss. Intact overlying external limiting membrane may be a prerequisite for this recovery.53,64

Treatment

Anti-VEGF Until very recently, effective treatment options for MacTel have been extremely limited. In patients without SNV, intravitreal anti-vascular endothelial growth factor (VEGF) injections have shown little efficacy and are not routinely used. One study including six eyes treated with two monthly bevacizumab injections and further injections as needed did report improved BCVA by an average of 7.9 letters at 18 months. Anatomic improvement was seen with decreased parafoveal leakage on FA and decreased OCT central macular thickness (CMT), although thickness rebounded later in the treatment course.65 Overall reductions in FA leakage and retinal thickness have been reported in several other small studies which showed no BCVA improvement with anti-VEGF in non-proliferative MacTel.66-67 One study using a monthly ranibizumab protocol over 12 months showed that at five-year follow up, far more of the nine treated eyes had decreased BCVA, new scotoma, or new SNV compared to untreated fellow eyes.68 These possibly detrimental results have not been reported elsewhere, but VEGF itself has been shown to play a fundamental role in Müller cell and photoreceptor survival, raising questions about whether anti-VEGF may be harmful in MacTel without active neovascularization.69 In contrast, MacTel patients who do have SNV based on FA or OCTA have been shown to benefit from anti-VEGF therapy. Though no randomized controlled trial has been performed to date, a majority of observational and cohort studies report significant improvement in BCVA along with decreased FA leakage and central retinal thickness across several anti-VEGF agents and treatment strategies.70-78 Laser and PDT Focal laser photocoagulation has generally been shown to cause no improvement in BCVA, and several case series have reported possible complications including new SNV.2,31,79 The use of subthreshold grid laser, or nondamaging retinal laser therapy, has been reported in a total of 21 eyes with MacTel across two studies by the same group. Pulse energy was titrated for each patient based on 30% of that required to create a visible burn outside the macula using Nd:YAG laser at 577 nm. A grid pattern of subthreshold laser was then applied over involved areas of the macula as determined by OCT and FAF. The area of EZ disruption decreased by 34% in treated patients compared to a 24% increase in the sham control group (p=0.029). However, there was no significant difference in BCVA or microperimetry at one year.80 In the uncontrolled study, BCVA improved from an average of 20/40 to 20/25 at one year.81 Patients underwent re-treatment at six months.80,81 Photodynamic therapy (PDT) yielded little benefit in the treatment of MacTel even with SNV. Multiple studies have reported stable, but not improved, BCVA in patients with neovascularization, and multiple patients required four to five sessions of PDT to achieve an enduring improvement in leakage on FA.82-84

2026 Harvard Ophthalmology Residents’ Course Cell-Based Gene Therapy Revakinagene taroretcel (NT-501, proprietary name ENCELTO, Neurotech Pharmaceuticals), an encapsulated cell therapy which is surgically implanted in the vitreous for sustained release of CNTF, was approved by the FDA for treatment of MacTel in March 2025.7 The implant contains bioengineered CNTFsecreting human RPE cells surrounded by a semipermeable membrane. This device was previously studied in RP and geographic atrophy. Testing of explanted devices from patients in these past trials suggests that CNTF release continues at a steady rate for at least 14.5 years.85 The implant is surgically placed in an operating room environment via a 2.0-mm sclerotomy in the pars plana.86 Implants are sutured to the sclera via a titanium anchor loop on the implant, then the sclerotomy and conjunctiva closed with sutures.87 Two identical phase 3 randomized controlled trials (referred to here as trial A and trial B), including a total of 228 patients with nonproliferative MacTel, were conducted. Patients with baseline EZ loss area between 0.16 and 2 mm2 based on en-face OCT were included. Patients with SNV or OCT hyperreflectivity suggestive of intraretinal neovascularization were excluded, as were patients with baseline BCVA worse than 20/80. One eye of each patient was randomized to receive either NT-501 or a sham procedure consisting of conjunctival incision and closure only. Baseline EZ loss area was slightly higher in both treatment groups than sham groups. Between both trials, participants were 88% White.88 The primary outcome was the rate of change of area of EZ loss on SD-OCT at 24 month follow-up. The primary intention-to-treat analysis was performed using a linear model, with EZ loss area as the dependent variable. In trial A, EZ loss area had grown 0.075 mm2 from baseline for treatment patients vs. 0.166 mm2 for sham patients (p < 0.001). That is, EZ loss expanded 54.8% less in the treatment group. In trial B, the rate of EZ loss area was also significantly lower in the treatment group, though the relative difference was lower at 30.6%. Subgroup analyses showed that, among patients older than 65 and patients with >0.5 mm2 of EZ loss at baseline, there was little difference in the rate of EZ loss between treatment and sham groups, suggesting that younger patients with less advanced disease had better treatment responses [supplemental data]. Patients with diabetes had a greater difference in rates of EZ loss between treatment groups than those without, although it is unclear whether there were confounding demographic variables.88,89 Aggregate retinal sensitivity, defined as the difference between microperimetry sensitivity within and outside of the scotoma corresponding to EZ loss, was assessed as a secondary outcome. Loss of aggregate sensitivity was significantly lower in the treatment than sham group in trial A. In trial B, aggregate sensitivity loss was slightly lower in the treatment group but did not achieve significance. Change from baseline BCVA was not analyzed as an outcome, but mean change in BCVA was +0.2 and -0.3 letters in the treatment groups and -0.6 and -1.7 letters in the control groups [supplemental data]. Change in reading speed and change in NEI-VFQ scores were not significantly different between groups in either trial. Device extrusion was reported in one patient and suture-related complications in five treated patients. Delayed dark adaptation, a tracked complication which was self-reported but not formally measured, developed in 24 treated patients (20.5%) and no sham patients.88 In the previous phase 2 trial, ERG under scotopic conditions showed reduced B-wave amplitude at six months in all treated patients, but in that study, dark-adapted ERG normalized by 24 months.87 The deficit in dark adaptation in treated patients warrants further study. This new therapeutic option has prompted excitement in the field. Particularly given scant previous options, the anatomic results in these trials are encouraging. The chief limitation of these trials is the lack of convincing functional results: differences in microperimetry outcomes after treatment were seen in one identically designed trial but not the other, and there were no significant differences in reading speed or patient-reported visual quality of life. The authors do not propose an explanation for the between-trial difference in retinal sensitivity; it is unclear if clinical site distribution differed between trials and could have led to differences in patient makeup or methodologies, especially given the challenges and variability inherent in visual field assessment. While EZ loss has been correlated with functional outcomes, including microperimetry in past studies, treating patients with an invasive and costly therapy based on surrogate rather than functional outcomes represents a quandary.38,90 The 24-month follow-up period is also relatively short for this slowly progressive disease: phase 4 monitoring and further large

Munsell, Mary studies will be of particular importance in determining the degree of meaningful benefit to patients and identifying which patients are likeliest to benefit. Perhaps longer-term studies will identify functional, including subjective, benefits in line with the anatomic benefits of revakinagene taroretcel.

Current and Future Therapeutic Studies

Other CNTF-Directed Therapies A study on implantation of revakinagene taroretcel (NT-501) in the fellow eyes of participants in the phase 2 and 3 trials discussed above has recently concluded. An ongoing phase 1 trial is assessing the same therapy, but with the membrane surrounding the encapsulated cells produced by a different manufacturer.91 Gene therapy for delivery of CNTF has been used in animal models of RP and other retinal degenerations with positive neuroprotective effects.25,26,92 There have been no human trials of gene therapy for MacTel. Intravitreal or subretinal injection of a viral vector or other gene therapy platform would be a potential alternative strategy to revakinagene taroretcel, although, like the cell-based implant, a subretinal approach would require intraocular surgery. Likewise, no trials have evaluated intravitreal injection of exogenous CNTF for a therapeutic paradigm similar to anti-VEGF injections; it is possible the pharmacokinetics and duration of effect would be limiting. Exogenous CNTF injection has been shown to have a neuroprotective effect in animal models of retinal disease, although functional results and duration of anatomic effects are variable.24,25,93 Systemic Therapy As the role of amino acid metabolism and sphingolipid accumulation in the pathogenesis of MacTel has emerged, systemic supplements and metabolism-directed therapies have been explored. Supplementation of lutein, mesozeaxanthin, and zeaxanthin, carotenoids thought to be protective for photoreceptors, showed no statistically significant preservation of photoreceptors or improvement in BCVA in 13 patients, although there were trends toward anatomic improvement on OCT.94 A phase 2a study for the SAFE trial (NCT04907084) is currently underway to assess the effects of systemic serine supplementation, fenofibrate therapy, and both on serum deoxysphingolipid levels in MacTel patients.91 Oral resveratrol, a polyphenol found in foods such as grapes, and associated with reduced cardiovascular disease risk, prevented formation of neovascular lesions in a mouse model resembling MacTel; this effect was mediated by decreased VEGF expression.95 Resveratrol has not been studied in humans for MacTel and relatively little investigation has been done in other human diseases. Resveratrol acts on many diverse and ubiquitous pathways and, at higher doses, may induce DNA damage and oxidation.96 Other Targets Anecortave acetate, a synthetic corticosteroid derivative which has no corticosteroid activity, but has angiostatic effects, was studied in a small pilot trial of seven eyes with both nonproliferative MacTel and SNV. Partial consolidation or regression of neovascularization was seen in all five eyes in the latter group, and all eyes had stable or improved BCVA. The drug was administered via posterior juxtascleral injection using a custom curved cannula.97 Production and study of this drug, which was also explored for neovascular age-related macular degeneration, was halted by the manufacturer. Potential Targets Other neurotrophic factors have shown promise in basic research. In a mouse model of MacTel-like pathology, intravitreal injection of a viral vector to activate Müller cell expression of neurotrophin-4 (NT4) improved photoreceptor survival and increased ERG signals compared to untreated controls.29 In a transcriptomic study identifying pathways potentially underlying deoxysphingolipid cytotoxicity in MacTel, addition of a small molecule (AA147) activating the ATF6 signaling arm of the unfolded protein response improved photoreceptor and Müller cell survival in retinal organoids exposed to toxic deoxysphingolipids. ATF6 activation also increased expression of mesencephalic astrocyte-derived neurotrophic factor (MANF), a neurotrophic factor expressed in Müller cells which has also been identified as protective against cytotoxicity.11

2026 Harvard Ophthalmology Residents’ Course

Conclusion MacTel is a not uncommon, neurodegenerative retinal disease characterized by secondary vascular changes, including neovascularization. Though the mechanism of damage in MacTel remains incompletely understood, significant progress has been made in the past 20 years in discovering molecular and genetic contributors, identifying and classifying clinical and imaging findings, and developing therapies. The revakinagene taroretcel CNTF-releasing implant represents the first therapy formally approved for MacTel. Further trials and real-world evaluation of this treatment will be crucial, as will continued work to generate and validate other treatment options.

Figures

Figure 1. Schematic diagram of the pathophysiology of macular telangiectasia type 2 (MacTel).

Munsell, Mary

Figure 2. Representative multimodal imaging – fundus photographs, fundus autofluorescence (FAF), fluorescein angiography (FA), and optical coherence tomography (OCT) – for: A-D) a 60-year-old female with moderate macular telangiectasia type 2 (MacTel) involvement. An atrophic patch within the superonasal macula shows hyperautofluorescence and early hyperfluorescence on FA. Diffuse late hyperfluorescence on FA is best seen in the temporal parafovea. OCT shows inner retinal cavitations as well as focal ellipsoid zone disruption at the fovea. E-M) a 56-year-old female with more advanced MacTel complicated by subretinal neovascularization (SNV). Two areas of SNV temporal and nasal to the fovea demonstrate leakage on FA. OCT shows a large zone of parafoveal outer retinal atrophy with temporal intraretinal hyperreflectivity as well as nasal subretinal hyperreflective material without subretinal fluid. HypoAF and hyporeflectance on blue confocal reflectance imaging (I) is seen temporally corresponding to pigment clumping. Distinct hyperreflectance is seen at the nasal SNV site on infrared (IR) reflectance imaging (J). B-scan (K) and en-face (L) views using OCT angiography (OCTA) shows telangiectatic vessel changes especially temporally and disruption of the typical foveal avascular zone. The avascular or outer retinal slab (M) shows the abnormal presence of nasal and temporal vessels corresponding to SNV. Images E-M courtesy of Dr. John Miller and Dr. Deeba Husain.

Figure 3. Diagrams of Revakinagene taroretcel (NT-501, proprietary name ENCELTO, Neurotech Pharmaceuticals); A) illustrating the implant components; B) within the eye after surgical implantation into the vitreous space.

2026 Harvard Ophthalmology Residents’ Course

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Munsell, Mary 23. Walsh N, Valter K, Stone J. Cellular and subcellular patterns of expression of bFGF and CNTF in the normal and light stressed adult rat retina. Exp Eye Res 2001;72:495-501. 24. LaVail MM, Yasumura D, Matthes MT, et al. Protection of mouse photoreceptors by survival factors in retinal degenerations. Invest Ophthalmol Vis Sci 1998;39(3):592-602. 25. Cayouette M, Gravel C. Adenovirus-mediated gene transfer of ciliary neurotrophic factor can prevent photoreceptor degeneration in the retinal degeneration (rd) mouse. Human Gene Ther 1997;8:423-430. 26. Rhee KD, Wang Y, Ten Hoeve J, et al. Ciliary neurotrophic factor-mediated neuroprotection involves enhanced glycolysis and anabolism in degenerating mouse retinas. Nature Comm 2022;13:7037. 27. Rhee KD, Nusinowitz S, Chao K, et al. CNTF-mediated protection of photoreceptors requires initial activation of the cytokine receptor gp130 in Müller glial cells. Proc Natl Acad Sci 2013;110(47):E4520-E4529. 28. Xie L, Yin Y, Benowitz L. Chemokine CCL5 promotes robust optic nerve regeneration and mediates many of the effects of CNTF gene therapy. Proc Natl Acad Sci 2021;118(9):e2017282118. 29. Dorrell MI, Aguilar E, Jacobson R, et al. Antioxidant or neurotrophic factor treatment preserves function in a mouse model of neovascularization-associated oxidative stress. J Clin Invest 2009;119(3):611-623. 30. Charbel Issa P, Gillies MC, Chew EY, et al. Macular telangiectasia type 2. Progr Retinal Eye Res 2013;34:49-77. 31. Engelbrecht NE, Aaberg TM, Sung J, et al. Neovascular membranes associated with idiopathic juxtafoveolar telangiectasis. Arch Ophthalmol 2002;120:320-324. 32. Heeren TFC, Chew EY, Clemons T, et al. Macular telangiectasia type 2: Visual acuity, disease end stage, and the MacTel area. MacTel Project Report Number 8. Ophthalmology 2020;127(11):1539-1548. 33. Gillies MC, Zhu M, Chew EY, et al. Familial asymptomatic macular telangiectasia type 2. Ophthalmology 2009;116:2422-2429. 34. Theelen T, Berendschot TT, Boon CJ, et al. Analysis of visual pigment by fundus autofluorescence. Exp Eye Res 2008;86:296-304. 35. Bottoni F, Eandi CM, Pedenovi S, et al. Integrated clinical evaluation of type 2a idiopathic juxtafoveolar retinal telangiectasis. Retina 2010;30:317-326. 36. Krivosic V, Tadayoni R, Massin P, et al. Spectral domain optical coherence tomography in type 2 idiopathic perifoveal telangiectasia. Ophthalmic Surg Lasers Imaging 2009;40:379-384. 37. Gaudric A, de Ducos LG, Cohen SY, et al. Optical coherence tomography in group 2A idiopathic juxtafoveolar retinal telangiectasis. Arch Ophthalmol 2006;126;807-811. 38. Heeren TFC, Kitka D, Florea D, et al. Longitudinal correlation of ellipsoid zone loss and functional loss in macular telangiectasia type 2. Retina 2018;38(S1):S20-S26. 39. Gass JD. Müller cell cone, an overlooked part of the anatomy of the fovea centralis: Hypotheses concerning its role in the pathogenesis of macular hole and foveomacular retinoschisis. JAMA Ophthalmol 1999;117(6):821-823. 40. Kim YH, Chung YR, Oh J, et al. Optical coherence tomographic features of macular telangiectasia type 2: Korean Macular Telangiectasia Type 2 Study — Report No. 1. Sci Rep 2020;10:16594. 41. Venkatesh R, Reddy NG, Mishra P, et al. Spectral domain OCT features in type 2 macular telangiectasia (type 2 MacTel): Its relevance with clinical staging and visual acuity. Int J Retina Vitreous 2022;8(1):26. 42. Karth PA, Raja SC, Brown DM, et al. Outcomes of macular hole surgeries for macular telangiectasia type 2. Retina 2014;34(5):907-915. 43. Krivosic V, Lavia C, Aubineau A, et al. OCT of outer retinal hyperreflectivity, neovascularization, and pigment in macular telangiectasia type 2. Ophthalmol Retina 2021;128(7):958-962. 44. Chew EY, Peto T, Clemons TE, et al. Macular telangiectasia type 2: A classification system using multimodal imaging; MacTel Project Report Number 10. Ophthalmol Sci 2022;3(2):100261.

2026 Harvard Ophthalmology Residents’ Course 45. Thorell MR, Zhang Q, Huang Y, et al. Swept-source OCT angiography of macular telangiectasia type 2. Ophthal Surg Lasers Imaging Retina 2014;45(5):369-80. 46. Gonzalez MA, Schechtman D, Haynie JM, et al. Unveiling idiopathic macular telangiectasia: Clinical applications of optical coherence tomography angiography. Eur J Ophthalmol 2017;27(4):e129-e133. 47. Chandran K, Giridhar A, Gopalakrishnan M, et al. Microvascular changes precede visible neurodegeneration in fellow eyes of patients with asymmetric type 2 macular telangiectasia. Eye 2021;36(8):1623-1630. 48. Tzaridis S, Wintergerst MWM, Mai C, et al. Quantification of retinal and choriocapillaris perfusion in different stages of macular telangiectasia type 2. Invest Ophthalmol Vis Sci 2019;60:3556-3562. 49. Zhang Q, Wang RK, Chen CL, et al. Swept source optical coherence tomography angiography of neovascular macular telangiectasia type 2. Retina 2015;35:2285-2299. 50. Breazzano MP, Yannuzzi LA, Spaide RF. Characterizing retinal-choroidal anastomosis in macular telangiectasia type 2 with optical coherence tomography angiography. Retina 2020;40(1):92-98. 51. Charbel Issa P, Finger RP, Helb HM, et al. A new diagnostic approach in patients with type 2 macular telangiectasia: Confocal reflectance imaging. Acta Ophthalmol 2008;86:464-465. 52. Ooto S, Hangai M, Takayama K, et al. High-resolution photoreceptor imaging in idiopathic macular telangiectasia type 2 using adaptive optics scanning laser ophthalmoscopy. Invest Ophthalmol Vis Sci 2011;52(8):5541-5550. 53. Litts KM, Okada M, Heeren TFC, et al. Longitudinal assessment of remnant foveal cone structure in a case series of early macular telangiectasia type 2. Transl Vis Sci Technol 2020;9(4):27. 54. Peto T, Heeren TFC, Clemons TE, et al. Correlation of clinical and structural progression with visual acuity loss in macular telangiectasia type 2: MacTel Project Report No. 6 – The MacTel Research Group. Retina 2018;38(S1):S8-S13. 55. Vujosevic S, Heeren TFC, Florea D, et al. Scotoma characteristics in macular telangiectasia type 2: MacTel Project Report No. 7—The MacTel Research Group. Retina 2018;38:S14-S19. 56. Charbel Issa P, Helb HM, Rohrschneider K, et al. Microperimetric assessment of patients with type II macular telangiectasia. Invest Ophthalmol Vis Sci 2007;48:3788-3795. 57. Heeren TFC, Clemons T, Scholl HPN, et al. Progression of vision loss in macular telangiectasia type 2. Invest Ophthalmol Vis Sci 2015;56:3905-3912. 58. Schmitz-Valckenberg S, Ong EEL, Rubin GS, et al. Structural and functional changes over time in MacTel patients. Retina 2009;29(9):1314-1320. 59. Szepessy Z, Barboni MTS, Nagy ZZ, et al. Retinal sensitivity and fixation stability changes during repeated microperimetry. J Clin Exp Ophthalmol 2017;8(6):1000697. 60. Charbel Issa P, Holz FG, Scholl HPN. Metamorphopsia in patients with macular telangiectasia type 2. Doc Ophthalmol 2009;119:133-140. 61. Clemons TE, Gillies MC, Chew EY, et al. The National Eye Institute Visual Function Questionnaire in the Macular Telangiectasia (MacTel) project. Invest Ophthalmol Vis Sci 2008;49(10):4340-4346. 62. Finger RP, Charbel Issa P, Fimmers R, et al. Reading performance is reduced by parafoveal scotomas in patients with macular telangiectasia type 2. Invest Ophthalmol Vis Sci 2009;50:1366-1370. 63. Raming K, Goerdt L, Begemann E, et al. Long-term progression of ellipsoid zone loss and associated features on optical coherence tomography in macular telangiectasia type 2. Ophthalmology 2025;online ahead of print. 64. Wang Q, Tuten WS, Lujan BJ, et al. Adaptive optics microperimetry and OCT images show preserved function and recovery of cone visibility in macular telangiectasia type 2 retinal lesions. Invest Ophthalmol Vis Sci 2015;56(2):778-786. 65. Charbel Issa P, Finger RP, Holz FG, et al. Eighteen-month follow-up of intravitreal bevacizumab in type 2 idiopathic macular telangiectasia. Brit J Opthhalmol 2008;92(7):869.

Munsell, Mary 66. Kovach JL, Rosenfeld PJ. Bevacizumab (Avastin) therapy for idiopathic macular telangiectasia type II. Retina 2009;29(1):27-32. 67. Toy BC, Koo E, Cukras C, et al. Treatment of non-neovascular idiopathic macular telangiectasia type 2 with intravitreal ranibizumab: Results of a phase II clinical trial. Retina 2012;32(5):996-1006. 68. Kupitz EH, Heeren TFC, Holz FG, et al. Poor long-term outcome of anti-vascular endothelial growth factor therapy in nonproliferative macular telangiectasia type 2. Retina 2015;35(12):2619-2626. 69. Nishijima K, Ng YS, Zhong L, et al. Vascular endothelial growth factor-A is a survival factor for retinal neurons and a critical neuroprotectant during the adaptive response to ischemic injury. Am J Pathol 2007;171(1):53-67. 70. Karasu B, Gunay BO. Comparison of anatomical and visual outcomes following different anti-vascular endothelial growth factor treatments in subretinal neovascular membrane secondary to type 2 proliferative macular telangiectasia. Graefe’s Arch Clin Exper Ophthalmol 2020;258:99-106. 71. Matt G, Sacu S, Ahlers C, et al. Thirty-month follow-up after intravitreal bevacizumab in progressive idiopathic macular telangiectasia type 2. Eye 2010;24(10):1535-1541. 72. Sen S, Rajan RP, Damodaran S, et al. Real-world outcomes of intravitreal anti-vascular endothelial growth factor monotherapy in proliferative type 2 macular telangiectasia. Graefe’s Arch Clin Exper Ophthalmol 2021;259(5):1135-1143. 73. Narayanan R, Chhablani J, Sinha M, et al. Efficacy of anti-vascular endothelial growth factor therapy in subretinal neovascularization secondary to macular telangiectasia type 2. Retina 2012;32(10):2001-2005. 74. Abdelaziz M, Rostamizadeh M, Schartman J, et al. The use of anti-vascular endothelial growth factor therapies in the macular telangiectasia associated with choroidal neovascularization. Invest Ophthalmol Vis Sci 2016;57(12):21455962. 75. Baz O, Yilmaz I, Alagoz C, et al. Efficacy of intravitreal bevacizumab in treatment of proliferative type 2 idiopathic juxtafoveal telangiectasia. Turk J Ophthalmol 2017;47(3):144–148. 76. Ozkaya A, Alkin Z, Karakucuk Y, et al. Long term result of intravitreal bevacizumab in a patient newly transformed to proliferative macular telangiectasia type 2. Middle East Afr J Ophthalmol 2013;20(4):360–362. 77. Toygar O, Guess M, Youssef D, et al. Longterm outcomes of intravitreal bevacizumab therapy for subretinal neovascularization secondary to idiopathic macular telangiectasia type 2. Retina 2016;36(11):2150–2157. 78. Roller AB, Folk JC, Patel NM, et al. Intravitreal bevacizumab for treatment of proliferative and nonproliferative type 2 idiopathic macular telangiectasia. Retina 2011;31(9):1848–1855. 79. Park D, Schatz H, McDonald HR, et al. Fibrovascular tissue in bilateral juxtafoveal telangiectasis. Arch Ophthalmol 1996;114:1092-1096. 80. Lavinsky D, da Silva MO, Chaves AE, et al. Functional and structural effects of nondamaging retinal laser therapy for macular telangiectasia type 2: A randomized sham-controlled clinical trial. Retina 2021;41(3):487-494. 81. Lavinsky D, Wang J, Huie P, et al. Nondamaging retinal laser therapy: Rationale and applications to the macula. Invest Ophthalmol Vis Sci 2016;57(6):2488-2500. 82. Potter MJ, Szabo SM, Sarraf D, et al. Photodynamic therapy for subretinal neovascularization in type 2A idiopathic juxtafoveolar telangiectasis. Can J Ophthalmol 2006;41(1):34-37. 83. Snyers B, Verougstraete C, Postelmans L, et al. Photodynamic therapy of subfoveal neovascular membrane in type 2A idiopathic juxtafoveolar retinal telangiectasis. Am J Ophthalmol 2004;137(5):812-819. 84. Hussain N, Das T, Khanna R, et al. One-year results of verteporfin therapy for subretinal neovascularization associated with type 2A parafoveal telangiectasia. Clin Ophthalmol 2007;1(4):483-488. 85. Kauper K, Nystuen A, Orecchio L, et al. Long-term durability of ciliary neurotrophic factor-releasing revakinagene taroretcel-lwey in individuals with retinal degenerative disorders. Invest Ophthalmol Vis Sci 2025;66(11):3. 86. Chew EY, Clemons TE, Peto T, et al. Ciliary neurotrophic factor (CNTF) for macular telangiectasia type 2 (MacTel): Results from a phase I safety trial. Am J Ophthalmol 2014;159(4):659-666.

2026 Harvard Ophthalmology Residents’ Course 87. Chew EY, Clemons TE, Jaffe GJ, et al. Effect of ciliary neurotrophic factor on retinal neurodegeneration in patients with macular telangiectasia type 2: A randomized clinical trial. Ophthalmol 2019;126(4):540-549. 88. Chew EY, Gillies M, Jaffe GJ, et al. Cell-based ciliary neurotrophic factor therapy for macular telangiectasia type 2. NEJM Evid 2025;4(8):EVIDoa2400481. 89. Duncan JL. Ciliary neurotrophic factor – A promising new therapy for macular telangiectasia type 2. NEJM Evid 2025;4(8):2500127. 90. Sallo FB, Peto T, Egan C, et al. The IS/OS junction layer in the natural history of type 2 idiopathic macular telangiectasia. Invest Ophthalmol Vis Sci 2012;53:7889-7895. 91. Clinicaltrials.gov [database online]. Bethesda, MD: National Library of Medicine; 2025. 92. Lipinski DM, Barnard AR, Singh MS, et al. CNTF gene therapy confers lifelong neuroprotection in a mouse model of human retinitis pigmentosa. Mol Ther 2015;23(8):1308-1319. 93. Li Y, Tao W, Luo L, et al. CNTF induces regeneration of cone outer segments in a rat model of retinal degeneration. PLoS One 2010;5(3):e9495. 94. Tan ACS, Balaratnasingam C, Yannuzzi LA. Treatment of macular telangiectasia type 2 with carotenoid supplements containing meso-zeaxanthin: A pilot study. Ophthalmic Surg Lasers Imaging Retina 2016;47(6):528535. 95. Hua J, Guerin KI, Chen J, et al. Resveratrol inhibits pathologic retinal neovascularization in Vldlr(-/-) mice. Invest Ophthalmol Vis Sci 2011;52(5):2809-2816. 96. Salehi B, Mishra AP, Nigam M, et al. Resveratrol: A double-edged sword in health benefits. Biomedicines 2018;6(3):91. 97. Eandi CM, Ober MD, Freund KB, et al. Anecortave acetate for the treatment of idiopathic perifoveal telangiectasia: A pilot study. Retina 2006;26:780-785.

Ong, Janice

RPE and Photoreceptor Transplantations and 3D Retinal Organoids: Where are we? Janice X. Ong, MD; John B. Miller, MD; and Demetrios Vavvas, MD, PhD

Abstract Acquired and inherited retinal degenerative conditions like retinitis pigmentosa, Stargardt disease, and age-related macular degeneration are leading causes of permanent vision loss. The late stages of these conditions are characterized by progressive photoreceptor and retinal pigment epithelium (RPE) dysfunction, leading to loss of these retinal layers and loss of central vision. Therapeutic options for these conditions are limited and do not restore visual function once atrophy has occurred. Transplantation of healthy RPE and/or photoreceptor cells has been explored in a small number of clinical studies as a potential way to restore visual function, although studies are small and evidence of efficacy is still sparse. This review discusses current clinical studies in RPE and photoreceptor transplantation.

Introduction Retinal degenerative conditions are a leading cause of permanent vision loss and represent a key potential therapeutic target for regenerative medicine and particularly for photoreceptor and retinal pigment epithelium (RPE) transplantation. Age-related macular degeneration (AMD) is the most common retinal degeneration and a leading cause of blindness globally in patients aged 55 and older.1 While the exact pathogenic mechanisms underlying AMD are still debated, AMD is generally thought to result from a combination of genetic predispositions and cumulative oxidative stresses to the RPE, resulting initially in the formation of drusen, which are mixed lipid and protein deposits between the RPE and Bruch’s membrane.2 Advanced AMD has two subtypes: exudative (or wet), which is characterized by choroidal neovascularization (CNV); and geographic atrophy (GA), in which chronic inflammation is thought to lead to progressive photoreceptor and RPE loss manifesting as atrophic lesions.3 While visual outcomes in wet AMD have improved with the introduction of therapies such as anti-VEGF, which can regress neovessels and reduce vascular leakage,4, 5 eventual fibrosis of CNVs and underlying RPE dysfunction can still lead to loss of photoreceptors and permanent vision impairment.6 On the other hand, current treatments for GA such as pegcetacoplan and avacincaptad pegol, which are based on complement inhibition, are primarily shown to slow progression of atrophy and have not been shown to improve vision.7, 8 A number of early clinical studies have investigated various approaches to RPE and photoreceptor transplantation in wet AMD and GA. However, these techniques are still in development, and early results, although promising from a safety perspective, remain visually disappointing. Early efforts in RPE and photoreceptor transplantation have targeted not only AMD but also inherited retinal diseases (IRD) including retinitis pigmentosa (RP) and Stargardt disease, in which genetic mutations lead to abnormal development or function of the photoreceptors or RPE, resulting in vision loss. RP, a rod dystrophy, is the most common IRD and encompasses a group of causative genes that generally results in initially peripheral photoreceptor loss that progresses centrally, although there is significant phenotypic variation in the location and timing of RP presentation.9 Patients initially report nyctalopia in their earlier decades, and as photoreceptor and RPE loss progresses, go on to develop constriction of their peripheral visual field and eventually blindness when the central vision is involved. Stargardt disease is the most common inherited macular dystrophy and is caused by mutations in the ABCA4 gene, which encodes a retinal transporter that participates in the vitamin A cycle.10 Patients show accumulation of lipofuscin, a waste product indicating RPE and photoreceptor dysfunction and eventually progress to macular atrophy.11, 12 For IRDs, development of gene therapies to restore function to damaged photoreceptors is underway, and one treatment, voretigene neparvovec, has been FDAapproved for biallelic RPE65 mutation-associated retinal dystrophy.13 There are no FDA-approved treatments for Stargardt disease. However, photoreceptor and RPE restoration potentially provide an appealing gene-agnostic alternative.

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2026 Harvard Ophthalmology Residents’ Course This review compiles and discusses existing clinical studies in RPE and photoreceptor transplantation.

Methods This review considered case studies and clinical trials in RPE, photoreceptor, and photoreceptor precursor transplantation for which the results were published by peer-reviewed sources. We conducted searches using PubMed and Google Scholar to identify published RPE and photoreceptor transplantation studies using the search phrases “RPE transplantation,” “photoreceptor transplantation,” “retinal sheet transplant,” “stem cell RPE transplant,” “stem cell photoreceptor transplant,” and “retinal progenitor cell transplant” within the timeframe ranging from the inception of such transplantation studies in 1991 to December 31, 2025. Studies were then manually screened. Inclusion criteria were studies with human subjects who underwent transplantation procedures involving either RPE cells, photoreceptor cells, or retinal progenitor cells. Notably, we excluded studies that used other undifferentiated stem cells (such as mesenchymal cells). We also briefly discuss the results of several selected non-published trials in this manuscript, with the caveat that data for these studies is not peer-reviewed and limited to what has been reported in press releases or conference abstracts.

Clinical studies in RPE transplantation RPE cells serve multiple functions in the eye and intimately interact with their overlying photoreceptors, participating in recycling of cis-retinal in the visual cycle, providing nutrition to photoreceptors, and maintaining the blood-retinal barrier.14 RPE cells are an appealing target for transplantation for several reasons: they are resilient, do not require synaptic integration to function, are inherently located in the immune-privileged subretinal space, and, as cultured stem cells have emerged as another source of RPE, are relatively easy to differentiate and propagate.

Direct RPE cell transplantation Transplantation of RPE, although surgically complex, has been demonstrated with successful survival of the grafted tissue and in some cases short-term subjective visual improvement has been reported in patients with substantial central vision loss. This procedure has typically been studied in patients with choroidal neovascularization in whom visual prognosis was poor or in cases where treatments like PDT were unlikely to succeed, such as when RPE rip or extensive submacular hemorrhage are present; with the introduction of anti-VEGF therapy, it is now less often performed.15 In this approach, following vitrectomy, peripheral retinotomy, and removal of subfoveal choroidal neovascular membranes, RPE tissue from outside the diseased region is translocated to the submacular space.16, 17 Early studies by Peyman et al. and Algvere et al. attempted transplantation of allogeneic RPE patch grafts sourced from fetal and cadaveric tissue, respectively, in wet AMD with little success—the grafts typically failed without concurrent administration of systemic immunosuppression,18, 19 and in cases where anatomically successful grafting occurred, no visual acuity (VA) improvement was achieved.20, 21 While allogeneic tissue may be preferable in certain applications, for example in inherited retinal or RPE degenerative processes, autografted tissue is less likely to induce an immune response to the graft. Further studies used autografted RPE tissue from the peripheral retina, showing that the translocated RPE grafts demonstrated autofluorescence and achieved revascularization, suggesting that the grafts remained viable and retained some degree of RPE function.16, 17, 22 However, visual outcomes were mixed: Stanga et al. found in a series of nine eyes that underwent grafting of an RPE-choroid patch that, although patients were able to detect light within the grafted region at two-year follow-up, they showed no quantitative improvement in VA and fixation was subsequently lost at long-term follow-up at five to six years.23 Heussen et al., in a series of 30 eyes with CNV due to wet AMD that underwent a similar RPEchoroid patch graft, reported two or more lines of VA improvement in 5 (17%) of eyes at one year, while Joussen et al. reported a rate of 9% in a mixed group of wet and dry AMD eyes.24, 25 Binder et al., in a series of 39 eyes, used a modified approach in which RPE cells were scraped from the peripheral retina and injected subretinally.16 They found VA improved by two or more lines in over half of eyes at one-year

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Ong, Janice follow-up, as well as increased response on multifocal ERG in the transplant group relative to a control group that underwent CNV excision alone. However, the majority of eyes that registered improvement had undergone concurrent cataract surgery at the time of the procedure, raising the question of the extent to which VA improvement could be attributed to the transplant.26 Of note, while Stanga et al. used RPE grafts taken from structurally normal macula adjacent to the area of excised CNV, raising the question of whether RPE in those areas was subclinically diseased, subsequent studies by other groups used RPE tissue derived from the peripheral retina. Larger series in eyes receiving RPE patch grafts have reported subjective visual improvements in some patients.15, 27 Parolini et al. reported in a series of 88 eyes that 40% of eyes experienced VA improvement of over 15 ETDRS letters, or three lines of VA.15 Van Zeeberg et al., although they do not report individual changes in lines of VA, found that among a 130-eye group with mean pre-operative BCVA of 20/250, that 15% of eyes achieved BCVA better than 20/200, and 5% of eyes better than 20/40 at four years.27 More recently, Lu et al., in a series of 63 eyes that underwent translocation of either an RPE-Bruch’s membrane patch or RPE monolayer patch, reported VA improvement by two lines or more in 60% of eyes irrespective of graft type at two-year follow-up.28 Although most studies considered patients with CNV due to exudative AMD, transient visual improvements were also reported in cases with atrophic maculopathies such as geographic atrophy (GA) due to AMD.15, 29 While long-term data for RPE translocation in atrophic maculopathies is sparse, atrophy has been shown to recur at the graft site in eyes following macular translocation, a related procedure in which neuroretinal tissue from the macula is relocated to an area of functional RPE, raising the question of whether eyes that undergo RPE translocation are at risk of similar complications.30 The donor tissue retains the patient’s genetic predispositions and may already have accumulated degenerative changes associated with age or the underlying disease process, potentially limiting the graft’s functional lifespan.31, 32 These surgeries are also associated with a high rate of complications. Proliferative vitreoretinopathy (PVR) and associated retinal detachments were one of the most commonly reported complications.15, 24, 25, 27, 33 Recurrence of CNVs was also seen in some studies.15, 24, 33 Other complications included retinal hemorrhages, epiretinal membrane, macular holes, and failure of the graft to revascularize.29 The maximum size of the graft is also limited by the inherent trauma of the graft harvesting process to the peripheral retina, which releases RPE cells into the vitreous and thus increases the risk of complications like PVR.

RPE transplantation with stem cells Given the surgical risks and inherent graft size limitations associated with harvesting a peripheral RPE autograft, stem cells have been increasingly studied as a potential source of transplantable RPE. The eye is considered an immune-privileged organ due to the blood-ocular barrier, making it an attractive target for stem cell therapy.34 The structural and functional status of an intra-ocular graft can be closely monitored through multimodal imaging and testing including perimetry, angiography, and optical coherence tomography (OCT).35 However, given that the RPE itself forms part of the blood-retinal barrier, the barrier may be compromised in the conditions that RPE transplantation would seek to treat, which may put transplanted cells at risk of immune rejection. Additional concerns with stem cell therapy include the potential need for immunosuppression as well as tumorigenicity of the transplanted cells. Human embryonic stem cells Human embryonic stem cells (hESCs) are pluripotent cell lines derived from human embryonic tissue. The first FDA-authorized clinical trials involving hESC-derived products occurred in 2009; ocular hESCderived RPE transplantation trials were initiated subsequently in the early 2010s. Initial studies by Schwartz et al. (18 eyes) and Song et al. (4 eyes), using an approach in which a suspension of hESCRPE was subretinally transplanted into patients with either geographic AMD or Stargardt’s, demonstrated that the hESC-RPE cells were relatively well-tolerated with no serious adverse events and no evidence of graft rejection or abnormal proliferation.36, 37 Although their studies were not designed with visual outcomes as a primary endpoint, approximately half of their patients reported improvement in VA and vision-related quality of life.36, 38 While later studies by Mehat et al. (12 eyes), Li et al. (7 eyes), and Brant Fernandes et al. (12 eyes), using this surgical approach in patients with Stargardt’s, demonstrated a

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2026 Harvard Ophthalmology Residents’ Course similar safety profile, visual results were less promising, with no significant changes in VA or retinal sensitivity.39-41 Lv et al., in a series of 10 eyes with CNV secondary to wet AMD, reported significant (two lines or better) VA improvement in 5 eyes, although their patients underwent concurrent CNV removal alongside hESC-RPE cell transplantation.42 Adverse events in the above studies were generally considered mild and attributable to systemic immunosuppression, which was typically discontinued after weeks to months depending on study protocol. While development of ERM was frequently noted (ranging from 8 to 100% of eyes, although interpretation of this data is limited by the low case numbers per study), potentially attributable to deposition of RPE cells on the inner retinal surface, no eyes in the above studies were reported to have developed retinal detachments. A small number of studies have attempted delivery of hESC-RPE as sheets rather than in suspension, which preserves the polarity of the RPE cells, and may improve consistency and degree of coverage of the recipient area with grafted cells. Animal studies have also suggested improved survival of RPE cells when transplanted as sheets rather than suspension.43 Previous trials using suspended RPE cells relied on supine positioning to help distribute cells over the intended recipient region, but distribution of the cells was clumped and uneven. Da Cruz et al. performed transplantation of an hESC-RPE monolayer on a polyester membrane coated to simulate basement membrane in two patients with wet AMD. Using multimodal imaging, they showed reconstitution of an RPE-like band on OCT suggesting donor replacement of the previously damaged RPE. They reported no serious adverse events, and greater than two-line VA improvement that persisted to two years for one patient and five years for the second.44, 45 A clinical trial by Kashani et al. performed implantation of an hESC-derived RPE monolayer on a parylene substrate in 15 patients with GA, finding that despite using HLA-unmatched donor tissue, the implants remained in the same position at up to three-year follow-up and that patients showed no evidence of antibodies against the mismatched HLA of the donor with a two-month course of systemic immunosuppression.46, 47 Histologic studies in a subject who had become deceased for reasons unrelated to the study further showed that allografted RPE cells persisted for two years with no cellular findings to suggest rejection after the procedure.48 However, their approach reported more adverse surgical complications including retinal detachment and retinal hemorrhage in four eyes, potentially due to the larger retinotomy size required to insert the implant.47 Induced pluripotent stem cells The use of human embryonic stem cell lines is controversial given their origins from early-stage embryonic tissue, and alternative sources of stem cells are being explored.49 Induced pluripotent stem cells (iPSCs) are derived from adult somatic cells that have been reprogrammed to pluripotency by expression of transcription factors collectively termed “Yamanaka factors,” first described by Japanese researcher Shinya Yamanaka.50 The resulting iPSCs can then be induced to differentiate into other cell types including RPE.51, 52 Sugita et al. first described that allogeneic iPSC-derived RPE (iPSC-RPE) cells from HLA-matched donors could be successfully transplanted subretinally.53 A suspension of iPSC-RPE cells was injected subretinally in five patients with wet AMD who were then followed for one year afterwards with eye exams and serologic testing. Although they found evidence of immune response by patient lymphocytes against the grafts in three of the five eyes, no clinical evidence of graft rejection was noted; however, no improvement in retinal sensitivity was achieved. Notably, only local immunosuppression with sub-Tenon’s and topical steroids was utilized in these patients. Subsequently, the same group, in a series of three patients, two with RP and one with dry AMD, demonstrated that strips of allogeneic iPSC-RPE tissue could be subretinally implanted, with evidence of engraftment on subsequent multimodal imaging.54 One patient reported subjective visual improvement and an increased National Eye Institute Visual Function Questionnaire-25 (NEI VFQ-25) score, although none of the patients demonstrated improvement in VA or retinal sensitivity assessed by microperimetry. These patients were not HLA-matched, requiring systemic immunosuppression with cyclosporine for 24 weeks afterwards—one patient showed signs of immune rejection following discontinuation of immunosuppressants that improved with restarting local immunosuppressants. Another patient with Leber’s congenital amaurosis, a severe form of RP, who received the same treatment experienced

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Ong, Janice surgical complications including an IOP spike post-operatively and development of ERM that required subsequent surgical removal.55 Clinical investigation of autologous iPSCs has been more limited due to the time and expense involved, as a separate cell line must be generated and tested for each patient. These limitations also confine potential applications to patients with chronic rather than acute visual loss. Using sheets of RPE produced from iPSCs, Mandai et al. transplanted an autologous iPSC-RPE graft in a patient with CNV due to polypoidal choroidal vasculopathy (PCV).56 While no VA improvement was measured in the patient, the grafted tissue showed no clinical signs of rejection, and imaging studies showed preservation of the external limiting membrane and outer nuclear layer overlying the graft with no recurrence of CNV. They also found no evidence of tumorigenicity in the cells prepared for graft.56 At four years, the graft remained vascularized without active leakage or imaging findings to suggest rejection; the overlying retina had begun to develop degenerative cystic changes.57 Other clinical trials using autologous iPSC-RPE are underway (e.g., NCT04339764), although published results are not yet available.58 The results of initial studies cautiously suggest that iPSC-RPE transplantation can yield a surviving graft and, even in allogeneic grafts, may not require long-term immunosuppression, although improvements in retinal sensitivity and visual function remain elusive. The advent of new technologies such as CRISPRCas9-based gene editing may in the future also facilitate autologous RPE transplantation in those cases in which healthy RPE cannot be as easily obtained, such as inherited RPE dystrophies.59 Adult-derived RPE stem cells Another potential source of stem cells includes the RPE itself, given that a subpopulation of RPE cells has been shown to have multipotentiality.60 These RPE stem cells can then be induced to re-differentiate back into RPE cells.61, 62 Recently, Rao et al. performed subretinal injections of RPE stem-cell derived RPE cells in six patients with GA, showing that the procedure was well-tolerated with no serious adverse events, evidence of graft rejection, or tumorigenicity.63

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2026 Harvard Ophthalmology Residents’ Course Table 1. Summary of clinical studies in RPE transplantation Trial ID/ Study type Institution Location Patients references Cadaveric and autologous RPE 19 Case study Louisiana State Univ. 18 Case Karolinska series Inst.

Cell source and format

Surgical approach

Immunosuppressi on

Key safety outcomes

Follow-up time

None

Rejection

10 mo.

None

Rejection (75%)

2-3 y

Systemic (6 mo)

Rejection (25%), ERM (17%), PVR/RD (25%), immunosuppressan t adverse effect (50%) Graft malposition (22%), PVR/RD (11%) MH (3%), PVR/RD (10%), CNV recurrence (5%) ERM (21%), PVR/RD (7%)

1y

US

1 wAMD

Allogeneic RPE-BM

Sweden

7 wAMD, 9 GA

Allogeneic fetal RPE patch (9 pts) or suspension (7 pts) Allogeneic cadaveric RPE sheet

Subretinal implantation Subretinal implantation or injection Subretinal implantation

20, 21

Case series

Washington Univ. in St. Louis

US

12 wAMD

17, 23

Case series

Moorfields

UK

9 wAMD

Autologous RPEchoroid patch

Subretinal implantation

None

16, 26

Consecutiv e case series RCT

Ludwig Boltzmann Inst. Ludwig Boltzmann Inst.

Austria

39 wAMD

Autologous RPE suspension

Subretinal injection

None

Austria

14 wAMD

Subretinal implantation or injection

None

15

Consecutiv e case series

Univ. of Padova

Italy

84 mixed disease group

Autologous RPEchoroid patch (7 patients) or suspension (7 patients) Autologous RPEchoroid patch

Subretinal implantation

None

22, 24, 25, 27, 65

Consecutiv e case series Consecutiv e case series Consecutiv e case series

Rotterdam Eye Hosp.

Netherland s

130 wAMD

Autologous RPEchoroid patch

Subretinal implantation

None

Rotterdam Eye Hosp.

Netherland s

12 GA

Autologous RPEchoroid patch

Subretinal implantation

None

Peking Univ.

China

63 wAMD

Autologous RPE monolayer (31

Subretinal implantation

None

NCT0040171 364

29

28, 33

ERM (5%), MH (3%), PVR/RD (11%), CNV recurrence (5%) PVR/RD (10%), CNV recurrence (10%) PVR/RD (42%)

2 y (5 pts), 5-6 y (4 pts) 1y 2y

2-10 y

1-7 y 6 mo-1 y

ERM (3%), PVR/RD (13%),

2y

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Human embryonic stem cells (hESC) NCT0134500 Phase I/II Advanced 6 Cell Tech NCT0134499 336

patients) or RPE-BM patch (32 patients)

CNV recurrence (5%)

US

9 SMD, 9 GA

RPE suspension from allogeneic hESC

Subretinal injection

Systemic (12 wks)

NCT0146983 239

Phase I/II

Astellas Pharma

US

12 SMD

RPE suspension from allogeneic hESC

Subretinal injection

Systemic (13 wks)

NCT0162555 937, 38

Phase I/II

CHA Biotech

South Korea

3 SMD

RPE suspension from allogeneic hESC

Subretinal injection

Systemic (13 wks)

NCT0167482 937

Phase I/II

CHA Biotech

South Korea

2 GA

RPE suspension from allogeneic hESC

Subretinal injection

Systemic (13 wks)

NCT0274973 441, 42

Phase I

Southwest Hosp.

China

RPE suspension from allogeneic hESC

Subretinal injection

Systemic (12 wks)

NCT0290357 640 NCT0228608 9 NCT0259069 246-48, 66

Phase I

Fed. Univ. of Sao Paulo OpRegen

Brazil

7 SMD, 10 wAMD 15 SMD 24 GA

Phase I/II

Calif. Proj. to Cure Blindness

US

15 GA

Subretinal injection Subretinal injection Subretinal implantation

Systemic

US, Israel

RPE suspension from allogeneic hESC RPE suspension from allogeneic hESC Allogeneic hESCderived RPE sheet on parylene substrate

NCT0169126 144, 45

Phase I

Moorfields

UK

2 wAMD

Allogeneic hESCderived RPE sheet on vitronectin substrate

Subretinal implantation

Systemic (peri-op), local

Japan

5 wAMD

RPE suspension from allogeneic HLAmatched iPSC

Subretinal injection

Local

Phase I/II

Induced pluripotent stem cells (iPSC) UMIN000026 Phase I RIKEN 00353

Systemic (8 wks)

Endophthalmitis (6%), ERM (6%), immunosuppressan t adverse effect (11%) ERM (8%), immunosuppressan t adverse effect (42%) Immunosuppressan t adverse effect (67%) ERM (100%), immunosuppressan t adverse effect (100%) CNV recurrence (6%)

2y

1y

3y 3y

1y (wAMD), 5 y (SMD) 1y

Retinal hemorrhage (20%), PVR/RD (7%), immunosuppressan t adverse effect (13%) ERM (100%)

3y

Rejection (20%), endophthalmitis (20%), ERM (40%)

1y

5y

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2026 Harvard Ophthalmology Residents’ Course JRCTa05020 012255 jRCTa05021 017854 NCT0433976 4

Case study Phase I/II Phase I/II

UMIN000011 Phase I 92956, 57 RPE stem cells NCT0462742 Phase I/II 863

VC Cell Therapy VC Cell Therapy Natl. Eye Inst.

Japan

1 LCA

Japan

2 RP, 1 GA Recruitin g

RIKEN

Japan

1 PCV

Luxa Biotech

US

6 GA

US

RPE suspension from allogeneic iPSC RPE strips from allogeneic iPSC Allogeneic iPSCderived RPE sheet on PLGA scaffold RPE sheet from autologous iPSC

Subretinal injection Subretinal injection Subretinal implantation

Systemic (6 mo) Systemic (24 wks)

Subretinal implantation

None

ERM

2y

Rejection (33%), ERM (33%)

1y

4y

RPE suspension from Subretinal Systemic 1y allogeneic RPE stem injection (6 mo) cells Abbreviations: BM = Bruch’s membrane, CNV = choroidal neovascularization, ERM = epiretinal membrane, GA = geographic atrophy, hESC = human embryonic stem cells, iPSC = induced pluripotent stem cells, LCA = Leber’s congenital amaurosis, MH = macular hole, PCV = polypoidal choroidal vasculopathy, PLGA = poly lactic-co-glycolic acid, PVR = proliferative vitreoretinopathy, RCT = randomized controlled trial, RD = retinal detachment, RP = retinitis pigmentosa, RPE = retinal pigment epithelium, SMD = Stargardt macular dystrophy, wAMD = wet AMD

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Considerations Methods of delivery While administering RPE cells in suspension has the advantages of potentially reducing trauma to the recipient tissue compared to grafting of a patch or sheet, the suspended cells may fail to graft into the anticipated location and may form clumps and aggregates rather than a monolayer.67 The cell suspension may reflux from the injection site into the vitreous, potentially leading to formation of epiretinal membranes and development of PVR.68 Additionally, RPE cells have an inherent polarity that is lost when the cells are suspended. RPE cells are typically bound to Bruch’s membrane via integrins, and loss of this polarity can result in RPE cell death or epidermal-mesenchymal transition, the latter of which is associated with fibrosis and development of PVR.69 In contrast, transplantation of RPE monolayers preserves the polarity and structural relationships of RPE cells to each other. Preclinical and animal studies suggest transplantation of RPE monolayers compared to suspension is associated with improved survival and functionality of the RPE cells.43, 70 Direct comparison of RPE cell vs. sheet transplantation in humans (14 eyes) found similar anatomic and functional outcomes with similar rates of complication (namely, ERM and PVR) between the two groups.64 However, this study used RPE cells sourced autologously rather than from stem cells, raising the question of the extent to which the graft harvesting process itself (of removing an intact RPE patch compared to scraping loose RPE cells from the patient’s peripheral retina) may have influenced their outcomes. Transplantation of RPE in sheets does not necessarily preserve the monolayer structure of RPE, with postmortem studies suggesting the transplanted RPE cells become disorganized and form rosette-like structures instead.21 The small number of human cases studied in clinical trials, as well as the surgical challenges of implanting large grafts, limit the generalizability of these conclusions at this time. Patient selection and stage of disease As RPE transplantation potentially expands beyond clinical trials in the future, patient selection will become increasingly important to optimize visual outcomes. Degenerative conditions such as AMD that affect the RPE cause not only RPE atrophy but also damage to—and eventually loss of—the overlying photoreceptors.32 Patients without sufficient photoreceptor reserve will not benefit from restoration of functioning RPE, a consideration which may have also limited visual outcomes in initial clinical trials, as these trials tend to recruit patients with end-stage disease. In studies where RPE damage was primarily due to CNV rather than atrophy, some degree of visual improvement may also be attributed to removal of the choroidal neovascular membrane rather than successful transplantation of RPE cells.42

Clinical studies in photoreceptor transplantation Many inherited retinal degenerations such as retinitis pigmentosa result in primary photoreceptor damage that cannot be fully addressed by RPE replacement alone. The interactions and metabolic pathways shared between photoreceptor and RPE cells also ensure that initially RPE degenerative processes result in eventual photoreceptor loss.71 For such patients, an approach to replace lost photoreceptors will be crucial. Compared to RPE transplantation, photoreceptor transplantation poses additional hurdles. For transplanted photoreceptor cells to provide additional function, they must not only structurally integrate with host RPE but also form synapses with host bipolar cells and interneurons. Producing sufficient photoreceptor cells for transplantation is also difficult, as photoreceptors, being terminal cells, do not divide, and other sources such as fetal tissue or retinal organoids are either controversial, do not scale in production, or are still in early development.72 Initial work in rodent models suggested that transplantation of fetal neural retinal cells could potentially regenerate photoreceptors that form apparent synapses with outer retinal cells and restore some light response.73-75 The structure and age of the grafts appeared to play a significant role in success of the grafts—younger donor grafts integrated better than older ones, and delivery of the grafts as suspended or aggregated cells was less successful than full sheets, with the suspended grafted cells either failing to survive or forming disorganized structures like rosettes.76-78 Transplantation as sheets rather than fragmented tissue also appeared to reduce the rejection risk of the grafts.79 Because retinal sheets still

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2026 Harvard Ophthalmology Residents’ Course contain donor interneurons and bipolar cells, the ability of the transplanted photoreceptors to integrate with the host tissue may be limited by their existing synaptic connections.80 Whether there was true integration of donor cells in these initial preclinical studies was also later called into question. Integration of the cells was presumed by histochemical tests showing presence of donor labels in the host tissues. However, subsequent studies suggested that materials transfer, or exchange of cellular contents between donor and recipient photoreceptors likely contributed to most of the apparent integration.81-83 Although animal studies in mouse models such as rd1 mice, which essentially fully lack rods, have shown recovery of a light response,84 which lends stronger support to integration of donor cells, these mice may still have residual cone function, of which cone “rescue” by the donor cells could still hypothetically produce a light response without requiring donor integration.85 Full integration of donor cells may not be required to provide some visual benefit, as materials transfer between donor and host may still have neuroprotective effects on the host retina (Fig. 1).

Figure 1. Proposed mechanisms in early photoreceptor transplantation studies. (A) Integration, where donor photoreceptors synapse with host cells, is the intended goal of photoreceptor transplants. (B) While initial animal studies of photoreceptor transplants were promising, the mechanism of materials transfer, where donor and host cells exchange contents, was found to be responsible for most of initial results. (C) However, while integration of donor cells remains elusive, transplanted cells can also exert neurotrophic effects on the degenerating host cells. This is the likely mechanism of jCyte, a retinal progenitor cellbased therapy currently in clinical trials.

Transplantation of retinal cells Kaplan et al. described the transplantation of cadaveric retinal sheets in two patients with RP in the late 1990s, finding that the grafts showed no evidence of rejection but also no visual benefit.86 Berger et al. used an excimer laser to harvest cadaveric photoreceptor sheets, which were then transplanted into eight patients with NLP vision due to RP, finding no evidence of graft rejection even without systemic immunosuppression but also no evidence of recovery of visual function.87 The use of autologous neural retinal tissue for transplantation has been explored for applications such as macular holes88 and AMD,89 but would not be applicable in diseases like RP, given there is no viable peripheral retinal tissue to graft by the time the disease has progressed centrally.

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Ong, Janice Other clinical studies explored the transplantation of fetal retina tissue, which is less immunogenic and contains retinal progenitor cells that eventually differentiate into photoreceptors. Das et al. (14 eyes) and Humayun et al. (9 eyes), using suspensions and aggregates, respectively, of fetal retina cells, demonstrated that subretinal transplantation of these cells was well-tolerated with no evidence of graft rejection or inflammation.90, 91 One patient developed a retinal detachment.90 However, while some patients experienced a possible transient increase in light sensitivity in the first few months, visual outcomes in both studies generally returned to baseline or worse by one year. Radtke et al. transplanted layers of fetal retina and underlying RPE subretinally into 10 eyes—six patients with RP and four with AMD—showing survival of the grafts at one-year follow-up without systemic immunosuppression.92, 93 Six patients experienced VA improvement in the surgical eye that was not correlated with microperimetry, and one patient sustained VA improvement over a six-year follow-up period with increased retinal sensitivity in the graft region.

Retinal progenitor cells Retinal progenitor cells (RPCs) are multipotent cells in the fetal retina that can differentiate into multiple cell types including photoreceptors and Müller glia.94 RPCs, unlike mature neural cells, retain the capacity to divide, and because they can give rise to both rods and cones, may be generalizable to a wider variety of retinal conditions. Liu et al. described the subretinal injection of fetal-derived RPCs in eight patients with advanced RP, finding that the transplanted cells appeared to be tolerated without any clinical evidence of rejection; about half of patients reported a transient increase in visual acuity at 2-6 months post-operatively that did not persist at 12 months and did not correlate to increased sensitivity on ERG.95 The company ReNeuron (Surrey, UK) conducted phase I/II clinical trials (clinicaltrials.gov identifier NCT02464436) where they studied the safety and efficacy of subretinally injected suspensions of RPCs in 29 patients with RP. Two groups—one receiving a lower dose of 1 million cells, the other receiving a higher dose of 2 million cells—were tested. While initial unpublished results were apparently promising, suggesting a mean 10-letter visual improvement at one year in lower-dose patients (unpublished data presented at Retinal Cell and Gene Therapy Innovation Summit, 2019), subsequent reports found these apparent visual improvements did not persist at two years. Higher-dose patients experienced a higher rate of surgical complications likely related to the larger volumes administered, and the trial was discontinued (press release, ReNeuron, 2022). jCyte (Newport Beach, CA), a stem-cell therapy company, is currently conducting clinical trials with an alternate approach in which RPCs are administered to patients with RP by intravitreal injection. Notably, this treatment was not designed with the intention for the injected cells to necessarily engraft, but rather to exert neurotrophic effects on the host retina. Their initial phase I/II results, reported by Singh et al. and Yang et al., showed that in 28 patients with RP, intravitreal injection of an allogeneic RPC suspension was well-tolerated and resulted in possible BCVA improvement of up to nine ETDRS letters for the highest dose group.96, 97 No ERMs or retinal detachments were reported. While intravitreal injection is a suboptimal delivery method for RPE cells due to the risk of PVR, these results suggest it may be a feasible approach for photoreceptor-directed therapies focused on neuroprotection and trophic effects.

Retinal organoids As stem cell technology has advanced, 3D retinal organoids derived from stem cells have emerged as another potential source of photoreceptors for transplant. Methods for generating retinal organoids, which contain multiple cell types that mimic the layered organization of the retina, were initially described by Nakano et al.98 Because organoids better approximate the microenvironment of the cells, including their synaptic connections, they have also been used as experimental models for studying retinal development and retinal degenerative conditions.99 However, production of retinal organoids remains challenging— culture times are long, there can be significant variation in structure and organization of the resulting organoids depending on culture conditions, and off-target differentiation of the precursor stem cells can reduce yields of the desired photoreceptors.100, 101 Histologic studies of transplanted retinal sheets derived from retinal organoids in rats also suggest that even organoid-derived tissue does not achieve full integration, and that disorganized structures such as rosettes are still seen.102 Additionally, in conditions

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2026 Harvard Ophthalmology Residents’ Course like RP, retinal remodeling results in the formation of a glial seal that may limit potential synaptic contact between the donor photoreceptors and host bipolar cells.103 Hirami et al., using allogeneic retinal organoids derived from iPSCs, demonstrated survival of the subretinal retinal organoid sheets over a follow-up period of two years in two patients with RP with no serious adverse events or evidence of abnormal proliferation.104 No clear evidence of visual function in the grafted sheets was found. More recently, Sumitomo Pharma, which manufactured the retinal organoid-derived sheets used in the study by Hirami et al., has begun a phase I/II clinical trial (clinicaltrials.gov identifier NCT06891885) in the US. The study is estimated to start recruiting patients at the end of 2025.

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Ong, Janice Table 2. Summary of clinical studies in photoreceptor and photoreceptor precursor transplantation Trial ID/ references

Study type

Institution

Location

Adult retinal sheet transplants (cadaveric and autologous) 86 Case Wash. Univ. US series in St. Louis 87 Phase I Wash. Univ. US in St. Louis 88 Case study Duke Eye US Ctr. 89 Case Inst. Clinico Italy, US series S. Anna, Duke Eye Ctr. Fetal neuroretinal cells 90 Phase I 91, 105

Phase I

LV Prasad Eye Inst. Johns Hopkins Univ. SOM

NCT0034591 Phase II Univ. of 792, 93 Louisville Retinal progenitor cells (RPCs) ChiCTRPhase I Southwest TNRCHosp. 0800019395 NCT0246443 Phase I/II ReNeuron 6 NCT0232081 296, 97

Phase I/II

jCyte

Patients

2 RP 8 RP 1 MH 6 wAMD

India

14 RP

US

8 RP, 1 wAMD

US

10 RP

China

8 RP

US

29 RP 28 RP

Induced pluripotent stem cell (iPSC)-derived retinal organoids NCT0689188 Phase I/II Sumitomo US Recruitin 5 Pharma g

Cell source and format

Surgical approach

Immunosuppressi on

Key safety outcomes

Follow-up time

Cadaveric retina sheets Cadaveric retina sheets Autologous retina sheet Autologous retina sheets

Subretinal implantation Subretinal implantation Preretinal implantation Subretinal implantation (5 patients), preretinal implantation (1 patient)

None

1y

None

1y

None

3 mo

None

Graft malposition (17%), ERM (17%)

3-19 mo

Fetal neuroretinal cells in suspension Fetal neuroretinal cell microaggregates (9 patients) and retinal sheet (1 patient) Allogeneic fetal retinaRPE sheets

Subretinal injection Subretinal injection or implantation

None

RD/PVR (7%)

12-40 mo

None

1y

Subretinal implantation

None

1-6 y

Allogeneic fetalderived RPCs in suspension Allogeneic fetalderived RPCs in suspension Allogeneic fetalderived RPCs in suspension

Subretinal injection

None

ERM (13%)

2y

None

Intraocular inflammation (25%)

1y

Allogeneic retinal sheets from iPSC-

Subretinal implantation

Subretinal injection Intravitreal injection

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2026 Harvard Ophthalmology Residents’ Course derived retinal organoids Abbreviations: ERM = epiretinal membrane, iPSC = induced pluripotent stem cells, MH = macular hole, PVR = proliferative vitreoretinopathy, RD = retinal detachment, RP = retinitis pigmentosa, RPC = retinal progenitor cells, RPE = retinal pigment epithelium, wAMD = wet AMD

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Bias and confounding in early transplantation trials Early transplantation trials have varied widely in their visual outcomes, with a small fraction of patients reporting subjective visual improvements, and other studies finding no changes in vision. However, quantitative measurements of retinal sensitivity (such as microperimetry or electroretinography) in these studies have generally not found convincing evidence of restoration of visual function from the grafts.54 Several aspects of study design may contribute to these apparent discrepancies and temper our interpretation of initially promising-appearing results. For example, concurrent cataract surgery26 or removal of CNVs42 performed at the time of the transplantation may have yielded improvement in visual acuity independent of the transplantation procedure. Some patients had received anti-VEGF either prior to surgery, or in the post-operative period after transplantation for persistent intra- or subretinal fluid, which may have also influenced visual acuity measurements.53 Another consideration is the contribution of practice effects in visual acuity testing, which may also produce an artifactual improvement as patients become more familiar with the testing method and conditions. Patients with AMD have also been shown to exhibit apparent improvements in vision despite advancing disease, which has been attributed to development of an eccentric fixation pattern to compensate for poor central vision.106, 107 These trials have been open-label, which may also introduce a potential placebo effect. Lastly, the sample size for these trials has been expectedly small, which also contributes to the variability of reported results.

Conclusions While we are still in early stages, initial studies suggest that the implanted tissue is tolerated in the recipients. Across published studies, no convincing signal of tumorigenicity or ectopic proliferation has emerged. However, clinically meaningful ocular surgical complications including retinal and subretinal hemorrhages, ERM, PVR, and retinal detachment, remain a key limitation and vary by delivery modality and surgical complexity. Evidence also suggests that there is the possibility of small visual improvement in a fraction of subjects. However, several considerations pose ongoing barriers to successful transplantation. Adverse reactions in the studies discussed appear to have been primarily related to systemic immunosuppression or complications of the surgeries themselves, although more severe surgical complications like PVR and retinal detachment are less common as surgical approaches have shifted away from large retinectomies and extensive removal of retinal or RPE tissue. There is also a tradeoff between the invasiveness of surgical approach and the organization of the donor tissue delivered (Fig. 2). For example, intravitreal injection would hypothetically be the least invasive approach for delivery. In clinical trials by jCyte, intravitreal injection of photoreceptor precursors potentially provided visual improvement in patients, through the intended mechanism of neurotrophic effects on the host. However, the likelihood of successful engraftment of intravitreally injected photoreceptors is very low, and this approach is not feasible in RPE transplantation due to the potential complications of free RPE cells escaping into the vitreous resulting in ERM and PVR.68 Subretinal implantation of donor cells, which inherently causes trauma to the retina through the necessary retinotomy site, also becomes more invasive as larger graft sizes (and sheets rather than suspensions) are delivered.

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Figure 2. Comparison of surgical approaches to RPE and retinal transplantation. Although allografted tissue has typically required systemic immunosuppression initially post-transplant, in all studies the courses of immunosuppression were relatively short, and structural incorporation of the grafts persisted despite lack of chronic immunosuppression, unlike other solid-organ transplants. However, some studies found serologic evidence of host antibodies directed against donor tissue, despite lack of clinical signs of rejection.53, 54 These results suggest that the subretinal space, which has been typically consider immune-privileged in healthy eyes, should not be assumed as such, especially in diseased eyes where the blood-retinal barrier is damaged or dysfunctional. The potential immunogenicity of allogeneic grafts remains a hurdle in the success of RPE and photoreceptor transplantations, leading some researchers to explore options like HLA-matched or hypoimmunogenic cell lines. However, while HLA-matching reduces the T-cell response to a graft, it does not eliminate immune responses via other pathways such as NK cells or minor histocompatibility complexes, which may also explain why studies using matched grafts showed evidence of immunogenicity.53 We also thus recommend that future trials include monitoring for donor-specific antibodies. Some patients have experienced transient increases in VA, and an even smaller number of patients has reportedly achieved sustained visual improvement across these trials,45, 92 but most patients have not shown evidence of visual function within the grafted tissue itself based on microperimetry or electroretinography.54, 90, 91 While these initial clinical studies were generally intended to demonstrate safety, not efficacy, these results raise the question of whether improved vision is truly attributable to the transplanted cells themselves, to testing effects, or potentially due to other aspects of the surgical approach such as concurrent cataract surgery or choroidal neovascular membrane removal, as we discuss above. The limited number of post-mortem histological studies suggests that transplanted cells, even when administered as sheets or on scaffolds to attempt to preserve the local retinal architecture, ultimately lose a normal adult differentiated structure, with RPE cells demonstrating loss of monolayer structure, clumping, migration, and fibrosis,48 and photoreceptors/retinal sheets forming disorganized rosettes and aggregates in the host,105 which may also contribute to a lack of meaningful function. No human trial to date has demonstrated synaptic integration of transplanted photoreceptors. The recently discovered phenomenon of materials transfer should also prompt a critical re-examination of visual outcomes in prior clinical trials, as it raises the question of whether apparent visual improvements identified in early retinal transplantation studies92, 93 were attributable to neurotrophic rescue of the host’s remaining cones rather than true graft function. Despite all these limitations, the mere fact that some cells integrate and some structural and functional metrics appear to improve suggest hope for the future of this approach. We are still far from the promised destination, but this is a needed stepping stone along the way. The volunteers who join these studies often give more to the public good than they receive, and they deserve our gratitude.

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Chen HC, Tzeng SS, Hsiao YC, Chen RF, Hung EC, Lee OK. Smartphone-Based Artificial Intelligence-Assisted Prediction for Eyelid Measurements: Algorithm Development and Observational Validation Study. JMIR MHealth UHealth. 2021;9(10):e32444. doi:10.2196/32444

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Lou L, Yang L, Ye X, et al. A Novel Approach for Automated Eyelid Measurements in Blepharoptosis Using Digital Image Analysis. Curr Eye Res. 2019;44(10):1075-1079. doi:10.1080/02713683.2019.1619779

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Liu Z, Tan K, Zhang H, et al. CT-based artificial intelligence prediction model for ocular motility score of thyroid eye disease. Endocrine. 2024;86(3):1055-1064. doi:10.1007/s12020-024-03906-0

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Lee J, Seo W, Park J, et al. Neural network-based method for diagnosis and severity assessment of Graves’ orbitopathy using orbital computed tomography. Sci Rep. 2022;12(1):12071. doi:10.1038/s41598-022-16217-z

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Lee J, Lee S, Lee WJ, Moon NJ, Lee JK. Neural network application for assessing thyroid-associated orbitopathy activity using orbital computed tomography. Sci Rep. 2023;13(1):13018. doi:10.1038/s41598-023-40331-1

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Moon JH, Shin K, Lee GM, et al. Machine learning-assisted system using digital facial images to predict the clinical activity score in thyroid-associated orbitopathy. Sci Rep. 2022;12(1):22085. doi:10.1038/s41598-022-25887-8

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Huang X, Ju L, Li J, et al. An Intelligent Diagnostic System for Thyroid-Associated Ophthalmopathy Based on Facial Images. Front Med. 2022;9:920716. doi:10.3389/fmed.2022.920716

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Shin K, Choung H, Lee MJ, et al. A Preliminary Evaluation of the Diagnostic Performance of a Smartphone-Based Machine Learning-Assisted System for Evaluation of Clinical Activity Score in Digital Images of Thyroid-Associated Orbitopathy. Thyroid Off J Am Thyroid Assoc. 2024;34(6):744-752. doi:10.1089/thy.2023.0621

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Yan C, Zhang Z, Zhang G, et al. An ensemble deep learning diagnostic system for determining Clinical Activity Scores in thyroid-associated ophthalmopathy: integrating multi-view multimodal images from anterior segment slitlamp photographs and facial images. Front Endocrinol. 2024;15:1365350. doi:10.3389/fendo.2024.1365350

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Hu H, Chen L, Zhang JL, et al. T2 -Weighted MR Imaging-Derived Radiomics for Pretreatment Determination of Therapeutic Response to Glucocorticoid in Patients With Thyroid-Associated Ophthalmopathy: Comparison With Semiquantitative Evaluation. J Magn Reson Imaging JMRI. 2022;56(3):862-872. doi:10.1002/jmri.28088

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Zhang H, Jiang M, Chan HC, et al. Whole-orbit radiomics: machine learning-based multi- and fused- region radiomics signatures for intravenous glucocorticoid response prediction in thyroid eye disease. J Transl Med. 2024;22(1):56. doi:10.1186/s12967-023-04792-2

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Morita D, Kawarazaki A, Soufi M, Otake Y, Sato Y, Numajiri T. Automatic detection of midfacial fractures in facial bone CT images using deep learning-based object detection models. J Stomatol Oral Maxillofac Surg. 2024;125(5S2):101914. doi:10.1016/j.jormas.2024.101914

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Bao XL, Zhan X, Wang L, Zhu Q, Fan B, Li GY. Automatic Identification and Segmentation of Orbital Blowout Fractures Based on Artificial Intelligence. Transl Vis Sci Technol. 2023;12(4):7. doi:10.1167/tvst.12.4.7

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Morita D, Kawarazaki A, Koimizu J, et al. Automatic orbital segmentation using deep learning-based 2D U-net and accuracy evaluation: A retrospective study. J Cranio-Maxillo-fac Surg Off Publ Eur Assoc Cranio-Maxillo-fac Surg. 2023;51(10):609-613. doi:10.1016/j.jcms.2023.09.003

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Kang D. Evaluating the Accuracy and Reliability of Blowout Fracture Area Measurement Methods: A Review and the Potential Role of Artificial Intelligence. J Craniofac Surg. 2023;34(6):1834-1836. doi:10.1097/SCS.0000000000009486

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Chepurnyi Y, Chernohorskyi D, Prykhodko D, Poutala A, Kopchak A. Reliability of orbital volume measurements based on computed tomography segmentation: Validation of different algorithms in orbital trauma patients. J CranioMaxillo-fac Surg Off Publ Eur Assoc Cranio-Maxillo-fac Surg. 2020;48(6):574-581. doi:10.1016/j.jcms.2020.03.007

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Hamwood J, Schmutz B, Collins MJ, Allenby MC, Alonso-Caneiro D. A deep learning method for automatic segmentation of the bony orbit in MRI and CT images. Sci Rep. 2021;11(1):13693. doi:10.1038/s41598-021-93227-3

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Wang G, Yang B, Qu X, et al. Fully automated segmentation and volumetric measurement of ocular adnexal lymphoma by deep learning-based self-configuring nnU-net on multi-sequence MRI: a multi-center study. Neuroradiology. 2024;66(10):1781-1791. doi:10.1007/s00234-024-03429-5

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Fu R, Leader JK, Pradeep T, et al. Automated delineation of orbital abscess depicted on CT scan using deep learning. Med Phys. 2021;48(7):3721-3729. doi:10.1002/mp.14907

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Duron L, Heraud A, Charbonneau F, et al. A Magnetic Resonance Imaging Radiomics Signature to Distinguish Benign From Malignant Orbital Lesions. Invest Radiol. 2021;56(3):173-180. doi:10.1097/RLI.0000000000000722

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Hou Y, Xie X, Chen J, et al. Bag-of-features-based radiomics for differentiation of ocular adnexal lymphoma and idiopathic orbital inflammation from contrast-enhanced MRI. Eur Radiol. 2021;31(1):24-33. doi:10.1007/s00330-02007110-2

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Bi S, Chen R, Zhang K, et al. Differentiate cavernous hemangioma from schwannoma with artificial intelligence (AI). Ann Transl Med. 2020;8(11):710. doi:10.21037/atm.2020.03.150

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Han Q, Du L, Mo Y, Huang C, Yuan Q. Machine Learning Based Non-Enhanced CT Radiomics for the Identification of Orbital Cavernous Venous Malformations: An Innovative Tool. J Craniofac Surg. 2022;33(3):814-820. doi:10.1097/SCS.0000000000008446

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Ren J, Yuan Y, Qi M, Tao X. MRI-based radiomics nomogram for distinguishing solitary fibrous tumor from schwannoma in the orbit: a two-center study. Eur Radiol. 2024;34(1):560-568. doi:10.1007/s00330-023-10031-5

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O’Shaughnessy E, Senicourt L, Mambour N, Savatovsky J, Duron L, Lecler A. Toward Precision Diagnosis: Machine Learning in Identifying Malignant Orbital Tumors With Multiparametric 3 T MRI. Invest Radiol. 2024;59(10):737-745. doi:10.1097/RLI.0000000000001076

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Fu R, Bandos A, Leader JK, et al. Artificial Intelligence Automation of Proptosis Measurement: An Indicator for Pediatric Orbital Abscess Surgery. Ophthalmol Ther. 2023;12(5):2479-2491. doi:10.1007/s40123-023-00754-5

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Parikh AO, Oca MC, Conger JR, McCoy A, Chang J, Zhang-Nunes S. Accuracy and Bias in Artificial Intelligence Chatbot Recommendations for Oculoplastic Surgeons. Cureus. 2024;16(4):e57611. doi:10.7759/cureus.57611

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Gernandt S, Aymon R, Scolozzi P. Assessing the accuracy of artificial intelligence in the diagnosis and management of orbital fractures: Is this the future of surgical decision-making? JPRAS Open. 2024;42:275-283. doi:10.1016/j.jpra.2024.09.014

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Amniotic Membrane and the Eye; A Review of Ophthalmic Applications Ayush A. Parikh MD; and John B. Miller

Introduction Human amniotic membrane (AM) has become increasingly integral for regenerative medicine, notably within ophthalmology as improved preparation and preservation techniques have enabled widespread availability. Since its first documented ophthalmic use in 1940 by de Rӧtth for conjunctival repair, the indications for AM have greatly expanded to include periocular wound repair, ocular surface reconstruction and healing, and vitreoretinal surgery.1 The growing interest in AM is owed to its intrinsic anti-inflammatory, anti-angiogenic, and anti-microbial properties. Indeed, a recent review of U.S. registered clinical trials from 2020-2023 revealed more than 90 studies investigating AM across many specialties within medicine.2 In this narrative review, we analyze the literature on ophthalmic applications of AM (Figure 1). We describe the biological and structural mechanisms underlying observed clinical outcomes, available preparations, current limitations and complications, and future innovations within AM transplantation (AMT).

Amniotic Membrane Structure and Biological Properties The human AM is a thin, pliable, and translucent tissue comprised of a single epithelial layer supported by a thick basement membrane and an avascular stroma (Figure 2). The basement membrane is composed of collagen types IV, V, and VII, fibronectin, and laminin-1 and -5, which provide tensile support and promote epithelial migration and adhesion.3,4 AM is also completely avascular and relies on surrounding amniotic fluid and surface blood vessels for nutrient supply in utero. This inherent avascularity in conjunction with expression of anti-angiogenic modulators, such as tissue inhibitors of metalloproteinases (TIMPs) and thrombospondin-1, makes AM particularly useful for corneal applications.5,6 Human AM expresses several key modulators of inflammation and fibrosis. Expression of TIMPs and down-regulators of pro-inflammatory cytokines such as interleukin-1 prevent migration of immune cells and subsequent destruction of native tissue.6,7 The suppression of transforming growth factor-beta (TGFβ) and its receptors prevents differentiation of fibroblasts into myofibroblasts and inhibits scar formation. This is particularly critical for maintaining tissue structure such as the ocular mucosal surface and preventing scarring in visually-significant disease processes such as proliferative vitreoretinopathy (PVR).8,9 Additionally, AM expresses various growth factors that underpin cellular regeneration and wound healing, including transforming growth factor-alpha and epidermal, keratinocyte, and basic fibroblast growth factors.10 These mechanisms in concert lead to the observed potent anti-inflammatory and anti-fibrotic properties of AM. Human AM has demonstrated moderate antimicrobial activity as it regulates the innate and adaptive immune system and potentially increases bioavailability of topically-applied antimicrobial treatments. Importantly, human AM expresses limited human leukocyte antigen class IA and IB antigens and does not express class DR isotypes, thereby conferring a low immunogenic profile that does not require immunosuppression when transplanted.11

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Amniotic Membrane Preparation and Available Formulations There are three main preservation methods for AM preservation following donor harvest: cryopreservation, lyophilization (freeze-dried), and dehydrated (heat-dried). While fresh AM is clinically viable, it is not widely used due to a narrow window of viability and logistical challenges in delivery, and has not been shown to be superior to preserved AM for ocular use.12 Cryopreserved AM is processed by sterilizing fresh donor tissue with antimicrobial irrigation followed by storage at -80°C in glycerol or dimethyl sulfoxide.13,14 This method enables storage for one to two years and maintains the structural integrity of the AM. An important step is minimizing crystallization during the freezing process, which can reduce the concentrations of growth factors and anti-angiogenic metabolites within the AM.15 In lyophilization, the AM is freeze-dried to form a dehydrated membrane that can be stored at room temperature and then rehydrated directly at time of use. Rapid freezing is typically followed by highvacuum dehydration, thereby removing the need for cold storage and increasing shelf-life. Dehydration is a similar method to lyophilization but utilizes low-temperature vacuum evaporation or even air-drying to eliminate the need for freezing the tissue. Lyophilization and dehydration processes may reduce some biological activity of the AM, although there is no consensus regarding whether this is suboptimal compared to traditional cryopreservation.14,16,17 In addition to the preparation methods above, amniotic membrane is available in different formulations, including fastened to a symblepharon ring, as sheets in various shapes and sizes, or most recently as AM extracts in topical drop formulations.

Clinical Applications in Eyelid and Periocular Surgery Eyelid and Fornix Reconstruction AMT has been described as a feasible alternative to traditional mucous membrane grafting for eyelid and fornix reconstruction, including for Stevens-Johnson syndrome (SJS), thermal and chemical burns, cicatricial pemphigoid, and graft-versus-host disease (GvHD). Notably, many of these conditions can present with systemic mucosal involvement and thus limit availability of grafting from traditional sites, such as the oral mucosa. Further, harvesting of oral mucosa increases surgical morbidity and operative time. Additionally, newer innovations such as ultra-thick AM grafts have expanded the use of AM in eyelid and fornix reconstruction. Compared to standard grafts that are typically 100 microns thick, 500-900 micron ultra-thick grafts offer greater tensile strength, surgeon manipulation, and durability.18–20 One of the most frequent applications of AM is in patients with socket contracture, who are at risk of developing fornix shortening and symblepharon, and as a result, cannot accommodate an ocular prosthetic. Both standard and ultra-thick AM grafts have been successfully described to address such deformities. There are several reports describing fornix lengthening in SJS, with two comparative interventional case series demonstrating greater socket volume and improved fornix depth compared to oral mucous membrane grafting.21–24 In the largest series to our knowledge investigating AMT in contracted sockets, 89% (n=16/18) patients were able to fit a prosthetic postoperatively.23 AMT can also be used in conjunction with mitomycin-C, oral mucous membrane transplantation, or with symblepharon ring on a case-by-case basis to improve surgical outcomes.25–27 Eyelid Malposition Cicatricial eyelid malposition includes both entropion and ectropion and can cause significant morbidity for patients. When the posterior lamella of the eyelid is involved, scar tissue must be released followed by placement of a spacer graft, for which AM is an option. The largest review to date describes five cases of cicatricial entropion after prior orbital surgery repaired with AM, with all patients showing excellent graft and eyelid position postoperatively, although recurrence was noted in two patients.28 AMT has also been utilized to cover bare tarsus after lid-splitting procedures for marginal entropion with keratinization. In one

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2026 Harvard Ophthalmology Residents’ Course prospective case series of 18 patients with cicatricial entropion, 88% (n=16) demonstrated surgical success with no trichiasis and with faster epithelization compared to non-AMT approaches.29 Other applications Additional applications for AM have been described for various extraocular and periocular indications. While limited to single case reports or small case series, AMT has been applied as a protective barrier in artificial ocular implant exposure and as an adjunct for reducing scarring after dacryocystorhinostomy and strabismus surgery.30–34

Clinical Applications for the Anterior Segment Conjunctival Surface AM is particularly useful in repair of mucosal tissues such as conjunctiva, as it provides a basement membrane scaffold that supports migration, adhesion, and differentiation of epithelial cells and goblet cells.35,36 This is further augmented by the aforementioned anti-inflammatory and anti-scarring properties of AM, which are crucial in maintaining homeostasis of the ocular surface. Typically, AM is implanted using fibrin glue and in an “epithelial-up” orientation to facilitate epithelial growth in surgical defects. One of the most frequent utilizations of AM is for conjunctival reconstruction, such as after pterygium or ocular surface squamous neoplasia resection. The largest case series investigating long-term outcomes of pterygium surgery with adjunct AMT and mitomycin C in 556 eyes found a 94.2% (n=523) singleoperation success rate with minimal complications.37 While conjunctival autografting has demonstrated superiority in regards to pterygium recurrence risk relative to AM, autologous grafting is not always feasible if donor sites have prior traumatic or postsurgical scarring.38 Interestingly, one study evaluated 493 eyes from patient populations with high-rates of pterygium recurrence that were treated with combined conjunctival autografting and subconjunctival AMT, and demonstrated a very low recurrence rate of 1.22% (n=6) over a follow-up period of 6 months to 6 years.39 While generalizability of results are limited due to the single institution and non-randomized nature of the study, combination repair approaches may provide the most efficacious outcomes in pterygium surgery in high-risk populations, although further rigorous comparative research is needed. AMT has also been shown to be effective for reconstruction after excision of neoplastic lesions, which can require exogenous tissue for large resections. A retrospective study by Agraval et al. reviewed outcomes of 53 cases with neoplastic conjunctival resections repaired with AM and found minimal scarring (11%), symblepharon (11%), and granuloma formation (7%), with zero cases of AM displacement or tumor recurrence over a 21 month follow-up period.40 Bulut et al. additionally showed high clinical efficacy and safety of AMT for ocular surface reconstruction in an entirely pediatric cohort.41 AM is a useful adjunct for conjunctival healing after chemical or thermal burn injury. AM can be sutured over the cornea and entire conjunctiva, including bulbar and both tarsal surfaces, effectively functioning as a biologic dressing. AM can also be anchored with a symblepharon ring, as these patients are at high risk of fornix contraction and symblepharon formation after burn injury. In the three large randomized control trials (RCTs) evaluating AM in thermal or burn injury, AM was typically deployed in a “basement membrane-up” orientation to facilitate reduced scarring and inflammation.42–44 Efficacy of AMT for chemical and thermal burn injuries was most recently reviewed in an Ophthalmology Technology Assessment by the American Academy of Ophthalmology, in which the literature is systematically reviewed for clinical efficacy and safety.45 The committee included nine high-quality studies and investigated the primary outcome of ocular surface re-epithelialization and the secondary outcome of visual acuity/corneal clarity. The authors concluded that AMT is particularly advantageous for earlier reepithelialization and defect closure compared to medical therapy alone. However, eyes with severe ocular burn injury based on standardized classification indices in general did not have any meaningful benefit from AMT versus standard therapy alone. This is consistent with the fact that conjunctival surface reepithelization is dependent on a functional supply of limbal stem cells, which may be absent or severely limited after significant burn injury and cannot be overcome by AM alone. The committee concluded that

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Parikh, Ayush further studies with better stratification based on limbal ischemia or stem cell population are needed to elucidate the role of AMT in severe burn cases. Cornea AMT is particularly useful for treatment of corneal injuries due to its avascularity and analogous structure to the anterior cornea. It has been used for corneal ulceration and perforation from a variety of etiologies, including neurotrophic ulcers, herpetic keratitis, bacterial keratitis, recurrent erosion syndrome, bullous keratopathy, and autoinflammatory diseases such as peripheral ulcerative keratitis.13,46–49 Neurotrophic keratopathy (NK) is a degenerative corneal disorder with compromised sensory innervation resulting in nonhealing epithelial defects and subsequent ulceration. AMT has been shown to have a 93% success rate of epithelial closure in NK, likely due to minimal inflammation in the often sterile ulcerative environment.50,51 Meaningful efficacy has also been reported in microbial ulcers (85% in bacteria, 80% in herpetic). A meta-analysis of 18 studies reviewing 390 eyes of 385 patients, including both infectious and non-infectious ulcer etiologies, demonstrated a pooled epithelial closure rate of 97%.51,52 In comparative studies of AM with antimicrobial treatment versus antimicrobials alone, AM has shown superior outcomes for long-term visual acuity, scar formation, and corneal neovascularization.53,54 Limbal stem cell (LSC) transplantation has become increasingly popular over the past few decades as improved understanding of limbal biology has led to safer and more efficacious surgery. Integral to these advances is the role of AM as a scaffold for outward migration of LSCs. In simple limbal epithelial transplant, a limbal biopsy from the donor site is placed onto amniotic membrane and then secured to the affected donor site. In cultivated limbal epithelial transplant, harvested limbal stem cells are sustained ex vivo on AM prior to transplant. In cultivated oral mucosal epithelial transplantation, harvested oral mucosa are seeded on an AM carrier substrate prior to transplant. All three techniques have demonstrated complete epithelization in cases of LSC deficiency and improvement in vision, although success rates vary across studies due to degree of LSC loss, the specific technique chosen, and etiology of injury.55–58 As discussed previously, AM is also useful for barrier protection and to reduce the risk of progressive corneal keratopathy and perforation from active inflammatory ocular surface disease, including from SJS and GvHD.44,59–61 Other innovative uses of AM include as a deterrent of pseudomembrane formation in chronic ligneous conjunctivitis, reducing corneal haze after refractive surgery, and promoting reepithelization after ethylenediaminetetraacetic acid chelation for band keratopathy.62–65 Glaucoma AM has been most studied as a surgical adjunct in glaucoma surgery. A systematic review that included 5 RCTs comparing trabeculectomy with and without AMT found significantly lower intraocular pressures (IOP) at 3 and 12 months with improved surgical success rate and without increased complications, although number of ocular antihypertensives remained similar before and after surgery.66 AMT has also been compared to conjunctival advancement for repair of late-onset filtering bleb leaks. While visual outcomes, IOP, and number of glaucoma medications were similar with both approaches, increased early re-leakage was noted in AMT cases, which may limit its use.67

Clinical Applications in the Posterior Segment AM has been validated in animal studies for supporting retinal pigment epithelium growth and inhibiting choroidal neovascularization, without inducing rejection or inflammation in the subretinal space.68–70 These encouraging findings motivated the first human clinical use of AM by Rizzo et al. for refractory macular holes (MHs).71 Since then, indications for AM have greatly expanded, including retinal detachment (RD) surgery with and without PVR, optic pit maculopathy, closure of posttraumatic scleral perforations, and age-related macular degeneration.72–74 Macular Hole Repair AM has been most well-studied in MH repair, particularly for large or recurrent holes. The original study by Rizzo et al. applied AM for recurrent MHs after failed conventional surgery and found a 100% closure rate (n=8/8), improved visual acuity, and no complications related to rejection or inflammation.71 Since

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2026 Harvard Ophthalmology Residents’ Course then, several similar studies have found closure rates between 91-100% for chronic and recurrent MHs, including for large MHs up to 1569 µm, and with a majority finding favorable visual outcomes.75–78A recent systematic review and meta-analysis assessing efficacy of AM for refractory MHs included eight studies aggregating to 103 eyes, all of which had failed primary pars plana vitrectomy and internal limiting membrane (ILM) peeling. Pooled analysis found rates of 66% visual improvement rate, 94% closure rate, and 3% complications of graft dislocation or contracture rate, with outcomes slightly improved in cryopreserved AM relative to dehydrated products.79 Although studies comparing AM to alternative approaches for MH repair are limited, one study found comparable rates of closure and improvement in visual acuity between AM and autologous ILM flaps, with AM superior for closure of large holes (>680µm).80 While further larger, standardized trials are needed, these studies suggest that AM can offer favorable anatomical and functional outcomes for management of refractory or large MHs. MHs in high myopia and the staphylomatous fundus pose a unique challenge for surgical repair, likely due to abnormal anatomy and altered biomechanical forces that increase surgical difficulty and risk of recurrence.81 Caporossi et al. assessed efficacy of AM in eyes with pathologic myopia (axial length >30mm) and reported a 93.7% (n=15/16) primary closure rate with visual improvement. Several studies have also trialed AM for combined MH and RD repair and found successful retinal reattachment and hole closure in the majority of cases.82–84 While limited to isolated case reports, AM has also been used for MH closure in eyes with severe inflammation including acute retinal necrosis and neuroretinitis.85,86 While larger, randomized studies are needed, AM appears to be a promising surgical adjunct in eyes with MH and abnormal anatomy such as high myopia or retinitis. Proliferative Vitreoretinopathy and Complex Retinal Detachment PVR is a challenging complication of RD surgery, characterized by excessive cellular proliferation and membrane formation that applies significant traction and prevents reattachment of the retina. Given that PVR is a dysregulated healing response to retinal trauma driven by TGFβ and other growth factors, AM is hypothesized to favor success in membrane removal due to its potent anti-inflammatory and antifibrotic properties that regulate the very same biochemical pathways.87,88 Several studies have included cases of PVR-related detachments treated successfully with AM-augmented vitrectomy approaches, with high retinal reattachment rates between 75-93%.84,89 AM has also been used to improve surgical outcomes for other types of complex RDs. Garcia-Vasquez et al. evaluated efficacy of a lyophilized AM patch for combined tractional and rhegmatogenous RDs in patients with advanced diabetic retinopathy. They found a 95.6% (n=22/23) surgical success rate without complications, although patients were only followed up to three months after surgery.90 Another study evaluated AMT in eyes with RD related to macular tears or advanced retinopathy of prematurity, and found anatomic success in all cases, albeit visual acuity did not significantly improve due to concurrent maculopathy.84 Surgical Technique and Complications The placement of AM can also be broadly characterized as epiretinal or subretinal, each with specific indications, surgical technique, and challenges. Subretinal placement involves creating a retinotomy followed by insertion of the folded AM graft using forceps or customized injector devices. Typically, the basement membrane side is positioned down.91 Histological analysis of AMT in porcine models has shown that the graft functions as a scaffold for glial cells which can promote closure of structural defects, although restoration of identifiable retinal layers was not seen.69 The largest study of subretinal AMT for complex MHs evaluated 30 eyes and found a closure rate of 73%, significant visual acuity improvement, and advantageous foveal structural changes at six month follow-up.92 Notably, the only study to utilize AMT for AMD-associated choroidal neovascularization utilized a subretinal AMT approach, presumably to directly oppose the anti-neovascular and anti-fibrotic graft with the neovascular pathology.93 Alternatively, AM can be placed in an epiretinal fashion, which involves peeling residual ILM around the structural pathology followed by placement of AM akin to a patch. This method promotes epiretinal gliosis and subsequent formation of a neuroglial bridge that promotes defect closure. This method has been theorized to also work effectively with tamponade agents to create a sealed microenvironment under constant tension from the adjacent gas or oil.94 Interestingly, one clinical study histologically examined

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Parikh, Ayush explanted epiretinal human AMT that was initially used for MH closure. The authors showed no retinal ingrowth from the graft itself upon removal and sustained preservation of retinal architecture and MH closure.95 Overall, epiretinal placement has been most frequently utilized for MH repair with high rates of closure, likely due to direct action of the AMT as a scaffold for cellular migration and facilitating closure at the inner retinal surface.4,82,96 The decision between subretinal versus epiretinal placement for MH repair is currently based on surgeon experience, as there have been no head-to-head, large-scale randomized studies directly comparing the two techniques. Notably, both techniques are not without complications. One concern with AM grafts is graft displacement or dehiscence. One study found a 23.3% (n=7/30 eyes) foveolar dehiscence rate with exposed AM in the subretinal space, although exposure area decreased over time and retinal reconstitution was noted in 3 of the 7 cases.92 For epiretinal placement, postoperative displacement of grafts has been reported with rates as high as 20%.96,97 Other concerns related to AM include whether graft integration structurally distorts the retina and disrupts central visual function. While rare, Patel et al. reported a case of epiretinal AM explantation due to integration of the graft into the inner retina and decreased visual acuity; after removal, the patient’s vision returned to baseline.95 Notably, subretinal AM placement was noted to cause parafoveal atrophy as early as one month after AMT in up to 40% of treated MH patients with high myopia, although this was not correlated with decreased visual acuity in affected cases and may be a unique complication in eyes with high axial length.98 Carla et al. reported a case of epiretinal AM patch contraction one year postoperatively that caused a localized, peripheral RD.99 Regardless of technique, AM graft placement for vitreoretinal surgery is notably difficult and carries risk for iatrogenic retinal injury, although epiretinal membrane formation rates were not higher compared to standard vitrectomy. Overall, complication rates appear low with AM use within vitreoretinal surgery.

Emerging Areas of Innovation AMT for ophthalmic use has undergone a significant evolution in the recent decades with expanded indications. A key area of inquiry is customization of amniotic membrane products for various ocular tissues. For example, ultra-thick amniotic membranes provide greater durability and are being explored as anterior segment patch grafts for scleral exposure from incisional glaucoma surgery, orbital implant exposure, and ocular surface neoplasia excisional defects.19,20,30,100 Another area of interest is improving ease of use of AM. One study evaluated sutureless AMT using a light-based protein bioadhesive in a rabbit animal model and found rapid and sustained attachment to the ocular surface.101 It is anticipated that ophthalmic use of AM will increase as different formulations clear regulatory hurdles and gain widespread commercial availability, including AM-derived topical formulations that have been used in ocular burn injury, keratopathy, and in conjunction with AMT to sustain treatment effect.102 Of interest are combined approaches using AMT with other placental-derived products that are also comprised of growth factors, anti-inflammatory cytokines, and neurotrophic factors. For example, umbilical cord serum has been used in conjunction with AM to successfully treat chronic dry eye disease, GVHD, and neurotrophic keratitis.103 In the posterior segment, AM with platelet-rich plasma or blood-clot assisted techniques may provide favorable outcomes in specific vitreoretinal contexts.91,104 A key step in validating the ever-growing indications of AM will be conduction of large, standardized, comparative clinical trials that can meaningfully assess outcomes and compare different AM preparations or surgical techniques. Currently, there is significant heterogeneity, including in graft preparation and size, orientation, technique, and concurrent procedures. A large majority of the existing research is limited to small case series or non-randomized comparative studies. While recent work has sought to develop consensus in specific use cases, further research is needed to develop definitive guidelines surrounding AM use within ophthalmology.

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Conclusion Human AM has been recognized as a valuable intervention for the treatment of ophthalmic disease, with wide-ranging indications across oculoplastics, anterior segment disease, and vitreoretinal surgery. AM provides unique biochemical and structural properties that support tissue healing, limits fibrosis, and reduces neovascularization. AM is available in multiple formulations with advances in surgical technique and preservation increasing its availability and shelf-life. Future studies that more effectively study the indications, outcomes, and complications of AM will guide the evolution of this rapidly-developing innovation.

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Peris-Martínez C, Menezo JL, Díaz-Llopis M, Aviñó-Martínez JA, Navea-Tejerina A, Risueño-Reguillo P. Multilayer amniotic membrane transplantation in severe ocular graft versus host disease. Eur J Ophthalmol. 2001;11(2):183186. doi:10.1177/112067210101100215

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Mohammadpour M, Maleki S, Hashemi H, Beheshtnejad AH. Recurrent Corneal Perforation due to Chronic Graft versus Host Disease; a Clinicopathologic Report. J Ophthalmic Vis Res. 2016;11(1):108-111. doi:10.4103/2008322X.180705

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Lee HK, Kim JK, Kim EK, Kim GO, Lee IS. Phototherapeutic keratectomy with amniotic membrane for severe subepithelial fibrosis following excimer laser refractive surgery. J Cataract Refract Surg. 2003;29(7):1430-1435. doi:10.1016/s0886-3350(02)02042-4

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Im SK, Lee KH, Yoon KC. Combined ethylenediaminetetraacetic acid chelation, phototherapeutic keratectomy and amniotic membrane transplantation for treatment of band keratopathy. Korean J Ophthalmol. 2010;24(2):73-77. doi:10.3341/kjo.2010.24.2.73

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Hondur AM. REPAIR OF THE EXIT WOUND OF A PERFORATING GLOBE INJURY WITH THE AMNIOTIC MEMBRANE: A SURGICAL ADJUVANT FOR EARLY VITRECTOMY. Retin Cases Br Reports. 2023;17(6). https://journals.lww.com/retinalcases/fulltext/2023/11000/repair_of_the_exit_wound_of_a_perforating_globe.31.asp x

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Celo Erdit, Whelan Ashley D, Seamone Christopher D, Gupta R. Rishi. Internal Plugging of a Traumatic Posterior Perforation Site Using Donor Sclera, Human Amniotic Membrane, and Fibrin Glue: A Novel Surgical Technique. J Vitreoretin Dis. 2023;7(6):536-539. doi:10.1177/24741264231195675

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Ferreira MA, Maia A, Machado AJ, et al. Human amniotic membrane for the treatment of large and refractory macular holes: a retrospective, multicentric, interventional study. Int J Retin Vitr. 2021;7(1):38. doi:10.1186/s40942021-00308-6

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Khaqan HA, Sahyoun JY, Haider MA, Buksh HM. AMNIOTIC MEMBRANE GRAFT FOR THE TREATMENT OF LARGE REFRACTORY MACULAR HOLE. RETINA. 2022;42(8). https://journals.lww.com/retinajournal/fulltext/2022/08000/amniotic_membrane_graft_for_the_treatment_of_large.9. aspx

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Bamberger MD, Felfeli T, Politis M, Mandelcorn ED, Galic IJ, Chen JC. Human Amniotic Membrane Plug for Chronic or Persistent Macular Holes. Ophthalmol Retin. 2022;6(5):431-433. doi:https://doi.org/10.1016/j.oret.2022.01.006

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Caporossi T, Pacini B, Bacherini D, Barca F, Faraldi F, Rizzo S. Human amniotic membrane plug to promote failed macular hole closure. Sci Rep. 2020;10(1):18264. doi:10.1038/s41598-020-75292-2

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Zhang H, Li Y, Chen G, Han F, Jiang W. Human amniotic membrane graft for refractory macular hole: A single-arm meta-analysis and systematic review. J Fr Ophtalmol. 2023;46(3):276-286. doi:10.1016/j.jfo.2022.07.001

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Lorenzi U, Mehech J, Caporossi T, et al. A retrospective, multicenter study on the management of macular holes without residual internal limiting membrane: the refractory macular hole (ReMaHo) study. Graefe’s Arch Clin Exp Ophthalmol = Albr von Graefes Arch fur Klin und Exp Ophthalmol. 2022;260(12):3837-3845. doi:10.1007/s00417022-05739-x

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Oleñik A, Rios J, Mateo C. INVERTED INTERNAL LIMITING MEMBRANE FLAP TECHNIQUE FOR MACULAR HOLES IN HIGH MYOPIA WITH AXIAL LENGTH ≥30 mm. Retina. 2016;36(9):1688-1693. doi:10.1097/IAE.0000000000001010

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Qiao G, Zhang XJ, Tang ZY, et al. Amniotic membrane for covering high myopic macular hole associated with retinal detachment following failed primary surgery. Int J Ophthalmol. 2022;15(5):760-765. doi:10.18240/ijo.2022.05.11

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Caporossi T, Governatori L, Gambini G, et al. Treatment of recurrent high myopic macular hole associated with retinal detachment using a human amniotic membrane. Jpn J Ophthalmol. 2022;66(6):518-526. doi:10.1007/s10384-022-00953-w

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Özdemir Zeydanlı E, Özdek Ş, Yalçın E, Özdemir HB. Human Amniotic Membrane: A Seal for Complex Retinal Detachments. Turkish J Ophthalmol. 2024;54(5):268-274. doi:10.4274/tjo.galenos.2024.56424

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Fossataro F, Parrulli S, Cereda MG. Retinal Detachment and Macular Hole in Acute Retinal Necrosis Treated with Human Amniotic Membrane. Ophthalmol Retin. 2025;9(10):e95. doi:https://doi.org/10.1016/j.oret.2025.02.012

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Erol MK, Gedik B, Suren E. Amniotic membrane transplantation in the treatment of macular hole secondary to neuroretinitis. J Fr Ophtalmol. 2025;48(5):104474. doi:https://doi.org/10.1016/j.jfo.2025.104474

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Tanihara H, Yoshida M, Matsumoto M, Yoshimura N. Identification of transforming growth factor-beta expressed in cultured human retinal pigment epithelial cells. Invest Ophthalmol Vis Sci. 1993;34(2):413-419.

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Caporossi T, Molle A, Carlà MM, et al. Applications of Human Amniotic Membrane Patching Assisted Vitrectomy in the Management of Postoperative PVR in Complex Retinal Detachments. J Clin Med. 2023;12(3). doi:10.3390/jcm12031137

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García-Vásquez Á, Rojas-Juárez S, Rios-Nequis G, Ramirez-Estudillo A. Lyophilised amniotic membrane patches are a safe and effective treatment for rhegmatogenous lesions in combined tractional and rhegmatogenous retinal detachment: a prospective interventional study. Eye (Lond). 2025;39(2):307-313. doi:10.1038/s41433-024-03411-8

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Chen YT, Lai CC, Hwang YS, Chen KJ, Wu WC. A Surgical Approach for Managing Refractory Macular Holes Using the Human Amniotic Membrane Patch Technique. Ophthalmic Surg Lasers Imaging Retina. 2024;55(10):613-616. doi:10.3928/23258160-20240411-04

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Choi M, Lee SH, Kim SW, Lee JY, Lee SJ. Foveal Configuration After Amniotic Membrane Transplantation in Complex Macular Holes. Retina. Published online May 2025. doi:10.1097/IAE.0000000000004528

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Caporossi T, Bacherini D, Governatori L, et al. Management of submacular massive haemorrhage in age-related macular degeneration: comparison between subretinal transplant of human amniotic membrane and subretinal injection of tissue plasminogen activator. Acta Ophthalmol. 2022;100(5):e1143-e1152. doi:10.1111/aos.15045

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Hillenmayer A, Strehle LD, Hilterhaus C, Ohlmann A, Wertheimer CM, Wolf A. Epiretinal Amniotic Membrane Influences the Cellular Behavior of Profibrotic Dedifferentiated Cells of Proliferative Vitreoretinopathy In Vitro. J Tissue Eng Regen Med. 2023;2023:8820844. doi:10.1155/2023/8820844

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Patel H, Swiatek K, Rivera-Zengotita M, Chen J. Human amniotic membrane graft removal and histopathologic evaluation following closure of a full thickness macular hole. Am J Ophthalmol Case Reports. 2025;37:102239. doi:https://doi.org/10.1016/j.ajoc.2024.102239

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Garcin T, Gain P, Thuret G. Epiretinal large disc of blue-stained lyophilized amniotic membrane to treat complex macular holes: a 1-year follow-up. Acta Ophthalmol. 2022;100(2):e598-e608. doi:10.1111/aos.14909

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Lin W, Chen H, Tang Y, Lin X, Wei Y. PRETREATED LYOPHILIZED HUMAN AMNIOTIC MEMBRANE GRAFT COVERING FOR RETINAL DETACHMENT WITH POSTERIOR RETINAL BREAKS ABOVE CHORIORETINAL ATROPHY IN PATHOLOGIC MYOPIA. Retina. 2024;44(6):974-981. doi:10.1097/IAE.0000000000004061

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Carlà MM, Mateo C. Contraction of a Giant Epiretinal Human Amniotic Membrane Patch Used to Manage a Highly Myopic Retinal Detachment Associated With Multiple Breaks. Ophthalmic Surg Lasers Imaging Retina. 2025;56(1):50-53. doi:10.3928/23258160-20240813-02

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Maeng SW, Park TY, Min JS, et al. Sutureless Transplantation of Amniotic Membrane Using a Visible Light-Curable Protein Bioadhesive for Ocular Surface Reconstruction. Adv Healthc Mater. 2021;10(13):e2100100. doi:10.1002/adhm.202100100

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Murri MS, Moshirfar M, Birdsong OC, Ronquillo YC, Ding Y, Hoopes PC. Amniotic membrane extract and eye drops: a review of literature and clinical application. Clin Ophthalmol. 2018;12:1105-1112. doi:10.2147/OPTH.S165553

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Daryabari SH, Ghasemian M, Lotfi E, et al. Placental-Derived Products for Corneal Regeneration: Applications of Amniotic Membrane, Cord Blood Serum, and Stem Cells: A Review. Transplant Cell Ther. Published online September 2025. doi:10.1016/j.jtct.2025.09.024

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Di Tizio F, Gattazzo I, Di Staso F, Di Pippo M, Guglielmelli F, Scuderi G. Human amniotic membrane patch and platelet-rich plasma to promote retinal hole repair in a recurrent retinal detachment. Eur J Ophthalmol. 2021;31(3):1479-1482. doi:10.1177/1120672120953314

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Beyond Intraocular Pressure: Clinical Perspectives on Neuroinflammation, Neuroprotection, and Neuroenhancement in Glaucoma Chhavi Saini, MBBS, MPH; Karen Liao; Dong Feng Chen, MD, PhD; Milica Margeta, MD, PhD; and Lucy Qing Shen, MD

Abstract Glaucoma is a chronic neurodegenerative disease in which progressive retinal ganglion cell (RGC) loss leads to irreversible vision loss. Although intraocular pressure (IOP) reduction remains the only proven modifiable risk factor for glaucoma, many patients continue to worsen despite well-controlled IOP, indicating pathogenic mechanisms beyond IOP-mediated injury. Here we synthesize laboratory, translational, and clinical evidence supporting neuroinflammation and immune dysregulation as central contributors to RGC vulnerability, with emphasis on glial activation (microglia, astrocytes, and Müller cells) and adaptive immune responses to autoantigens such as heat shock proteins. We then propose a clinically grounded framework that distinguishes neuroprotection (preventing further RGC injury) from neuroenhancement (restoring function of sick but still viable RGCs) and discuss how these concepts reshape interpretation of both failed and emerging clinical trials. We next review representative therapeutic approaches, including memantine, brimonidine, and nicotinamide for neuroprotection; trabeculectomy, CNTF-releasing encapsulated cell therapy (NT-501), and topical insulin for neuroenhancement; and early neuroinflammation-targeting strategies such as C1q inhibition (ANX007) and GLP-1 receptor agonists. Finally, we outline practical recommendations for future clinical trial design, including enrichment for biologically vulnerable progressors, integration of immune and neurodegeneration biomarkers, optimized functional testing strategies, and adoption of more sensitive structural and molecular endpoints. Collectively, these approaches provide a roadmap for developing novel therapies for glaucoma that extend beyond IOP control.

Article Neuroinflammation And Glaucoma: A Brief Introduction Glaucoma is a chronic neurodegenerative disease characterized by progressive retinal ganglion cell loss resulting in irreversible blindness.1 Although elevated intraocular pressure (IOP) remains the strongest and only modifiable risk factor for glaucoma, many patients continue to progress despite well-controlled IOP. In fact, normal tension glaucoma (NTG) comprises around one third of primary open angle glaucoma (POAG) patients,2 predominantly affecting patients with signs of local and systemic vascular dysregulation and manifesting as disc hemorrhages, nocturnal hypotension, migraine and Raynaud’s syndrome.3 In contrast, there are also patients whose optic nerves seem resistant to moderate IOP elevation (the so-called ocular hypertensives), as well as case reports of rare individuals who display remarkable resilience to exceptionally high IOPs present for years.4,5 Growing evidence demonstrates that glaucoma pathology extends beyond mechanical stress or IOPmediated injury.6 Neuroinflammation, immune dysregulation, neuroexcitotoxicity and growth factor deprivation are now recognized as key contributors to retinal ganglion cell (RGC) vulnerability and disease progression.7,8 Neuroinflammation involves the activation of resident glial cells and peripheral immune pathways which can produce a proinflammatory environment and promote RGC death (Figure 1).6,9 Clinical data support an immunologic predisposition contributing to glaucomatous vulnerability. In a large retrospective study, autoimmune diseases were significantly more prevalent among POAG patients, and an autoimmune diagnosis independently increased POAG risk by 2.6-fold.10 Trigger events leading to neuroinflammation are thought to include mechanical triggers such as IOP spikes or fluctuations. Similarly, inflammatory responses can arise due to vascular trigger events with low cerebral spinal fluid pressure, hypotension, abnormal autoregulation at the optic nerve head (ONH), and from

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2026 Harvard Ophthalmology Residents’ Course vascular compromise or focal disc hemorrhage.11,12 In addition, immune antigens such as glycosaminoglycans and heat shock proteins may trigger immune reactions.13 These antigens are recognized by microglia via toll-like receptors that act through the NF-κB signaling pathway.14 Once this innate immune activation is initiated, downstream pathways such as inflammasome assembly and cytokine production rapidly amplify the inflammatory response and further sensitize surrounding glial cells and RGCs to injury.15

Innate Immune System and Glial Activation Microglia and Other Myeloid Cells In the retina and optic nerve head, neuroinflammation, or the coordinated immune response to injury or stress, is driven primarily by resident glial cells, which serve as the innate immune gatekeepers.16 Resident myeloid cells in the central nervous system include microglia and border-associated macrophages, while monocyte-derived macrophages infiltrate in the settings of aging and disease.17,18 Previous studies have shown that myeloid cells reside in inner retinal layers and throughout the optic nerve head in the walls of large blood vessels and surrounding capillaries in glial columns and lamina cribrosa.19 Notably others have shown that early myeloid cell activation is seen before RGC loss in experimental glaucoma, 20 which includes a marked shift in morphological diversity, with a transition to hyper ramified, bushy, and amoeboid forms.16,17 In glaucoma postmortem eyes these ameboid microglia clusters have been found within the lamina cribrosa and around blood vessels, possibly interacting with a compromised blood-retinal barrier.21 Additionally, activated myeloid cells express MHCII and CD-200 in the ONH early in glaucoma, corresponding to ongoing axonal degeneration and disease progression.22–24 While microglia play critical roles in the normal development and homeostasis, they can become harmful in degenerative states by secreting inflammatory cytokines such as TNF-α, phagocytosing damaged but still living neurons, and activating other nearby cell types and thereby creating a proinflammatory environment.25 Microglial activation in the context of neuroinflammation and neurodegeneration has historically been described using a simplified binary framework, namely neurotoxic ‘M1’ microglia and neuroprotective ‘M2’ microglia.26,27 However, more recent work using single cell and bulk RNA sequencing has shown that microglia in neurodegenerative diseases such as Alzheimer’s disease, Amyotrophic Lateral Sclerosis and multiple sclerosis take on a so-called disease-associated microglial (DAM) phenotype marked by upregulation of genes such as Apoe, Lgals3, Spp1, and Gpnmb.28,29 Interestingly, our group has shown that microglia in mouse models of glaucoma also switch to a DAM molecular signature.30 One of the genes upregulated in microglia in glaucoma is Apoe, which codes for apolipoprotein E (APOE), the major lipoprotein in the brain. The APOE4 allele increases the risk of Alzheimer’s disease but decreases the risk of glaucoma.31 APOE is the key upstream regulator of the microglial DAM response in glaucoma, while a secreted inflammatory molecule Galectin-3 is an important downstream effector molecule, that can be targeted genetically and pharmacologically to prevent RGC loss in glaucoma.31 Notably, the APOE4 allele acts similarly to Apoe loss-of-function in terms of decreased microglial activation and improved RGC survival in animal models of glaucoma, thus providing a mechanistic explanation for why this allele is associated with a decreased risk of human glaucoma.32 Finally, APOE and Galectin-3 are upregulated in the retinal samples and the aqueous humor of glaucoma patients, suggesting that they may serve as biomarkers of neuroinflammation in glaucoma.30,33 Macroglia (Astrocytes and Müller cells) Retinal macroglia are composed of astrocytes and Müller cells. The retinal astrocytes reside predominantly within the nerve fiber layer and ganglion cell layer, where their processes contact RGC somata, axons, and superficial retinal vessels, forming a 3D gap-junction-coupled network.34 Through this architecture and other homeostatic functions they support axonal conduction and maintain the inner blood retinal barrier.34–36 Experimental glaucoma studies show that optic nerve head astrocytes undergo cytoskeletal remodeling and spatial reorganization without altering total glial coverage, suggesting redistribution rather than true gliosis.37–39 As axonal density declines in later disease, astrocytes proportionally expand within the nerve, likely due to hypertrophy.40 In the setting of inflammation, researchers have identified a reactive astrocyte subtype, namely “A1” astrocytes, which are triggered by microglia-derived IL-1α, TNF, and C1q (Figure 1).41 Unlike healthy astrocytes, A1 cells lose their supportive functions, such as promoting neuronal survival, axonal growth, and synapse formation, and instead become neurotoxic, contributing to the death of neurons

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Saini, Chhavi and oligodendrocytes. Importantly, saturated lipids contained in ApoE/ApoJ lipoparticles mediate astrocyteinduced toxicity.42 Müller cells span the full retinal thickness from the inner to outer limiting membranes, extending lateral processes that ensheathe all retinal neuronal somata and processes. They interface with the key compartments involved in molecular exchange, namely the retinal blood vessels, the vitreous body, and the subretinal space, forming the core of a columnar ‘micro-unit’ supporting retinal neurons.43 In human glaucoma, Müller cells demonstrate hypertrophy and increased number compared to controls.44 Experimental models demonstrate that Müller cell activation can stimulate microglial activation through ATP release and P2X7R signaling.45 Additionally authors have shown that elevated IOP can hyperactivate TRPV4 (a nonselective cation channel with wide expression in neurons, glia, and endothelial cells), causing calcium overload that induces Müller cell gliosis and release of cytokines like TNF-α that, in turn, mediate RGC apoptosis.46

Adaptive Immune System T cell Activation There is growing evidence that the adaptive immune system, particularly T-cell mediated responses, contributes meaningfully to glaucomatous neurodegeneration.47,48 Heat shock proteins (HSPs) have been identified as key autoantigens that drive this response. Intracellular upregulation of HSPs is initially protective, but extracellular release following cellular stress or injury acts as a “danger signal,” activating microglia which can act as antigen-presenting cells to stimulate HSP-specific T cells (Figure 1).47,49 Moreover, adoptive transfer of T cells from glaucomatous mice into healthy recipients triggers progressive RGC and axonal loss even without elevated IOP, demonstrating that autoreactive T cells can propagate injury independent of mechanical stress.47 Human studies support these findings. Our group has previously shown that peripheral blood analyses of patients with POAG exhibit heightened HSP-specific responses of helper type 1 T cells (Th1) to HSP27, and HSP60, with significantly higher IFN-γ production compared to controls, while HSP-specific Treg responses remained unchanged.48 Similarly other authors have demonstrated reduced regulatory T-cell frequencies and heightened proinflammatory CD4+ T-cell responses, suggesting that immune activation of T cells in glaucoma may occur without adequate immune regulation.50 B cell And Autoantibodies Growing evidence in humans suggests that serum levels of antibodies against several autoantigens are significantly elevated in POAG including NTG, compared with healthy controls.51,52 In particular, autoantibodies to HSPs, including alpha-crystallin and HSP-27, have been detected at higher titers in patients with NTG compared to controls.13 These autoantibodies may gain access to retinal tissues through parapapillary defects in the outer blood-retina barrier and can bind to ganglion cell layer antigens, potentially contributing to RGC apoptosis.53 Supporting this mechanism, experimental exposure of retinal tissue or cells to antibodies targeting small heat shock proteins was found to trigger apoptosis, leading to cell death.13 Furthermore, authors have shown that autoantibody reactivities in aqueous humor are nearly similar to those in serum of the same patients.52,54 Finally, although their exact pathogenic role remains unclear (whether causal, contributory, or merely secondary to neurodegeneration), these autoantibodies may serve as biomarkers for early detection or progression monitoring, especially in NTG.55

Neuroprotection And Neuroenhancement: A Conceptual Framework All of these innate and adaptive immune changes further solidify that glaucomatous damage is not driven by IOP alone. Instead, a complex interplay of mechanical, inflammatory, metabolic, and immune stresses ultimately converges to cause retinal ganglion cell death. In parallel, molecular mechanisms including glutamate mediated excitotoxicity, mitochondrial dysfunction, and calcium dysregulation further contribute to RGC injury.8,56,57

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2026 Harvard Ophthalmology Residents’ Course As we consider more effective therapeutic approaches for glaucoma, it becomes important to differentiate three related concepts, namely neuroprotection, neuroenhancement and neural regeneration (Figure 2). Neuroprotection refers to strategies that help prevent or protect the RGCs from ongoing injury independent of IOP control.58 Neuroenhancement focuses on improving the function of damaged RGCs that are still alive but not functioning appropriately.59 Neural regeneration, in contrast, would require actual regrowth and reconnection of damaged neurons, which remains a long-term goal for the treatment of glaucoma but is not yet clinically achievable.59 In the next section, we highlight therapies being developed with glaucoma neuroprotection and neuroenhancement in mind. We also briefly touch upon therapies in early stages of development that target neuroinflammation in glaucoma.

Potential Treatments Focusing on Neuroprotection Memantine Memantine was evaluated in the first large-scale clinical trial aimed specifically at testing a possible neuroprotective treatment in glaucoma. It is a widely used medication in several neurologic disorders, including Alzheimer’s disease, because it blocks NMDA receptor channels in a way that reduces harmful excitotoxicity.60 In a monkey glaucoma model, memantine treatment significantly reduced neuron cell body shrinkage in the lateral geniculate nucleus, the major innervation target for RGCs, compared with controls.61 Expected neuronal loss did not occur after induction of glaucoma in the treatment group compared to vehicle, suggesting memantine preserved neuronal structure.61 In a different preclinical study, memantine treatment was associated with preservation of optic cup morphology in animals with elevated IOP.62 However, the neuroprotective effect of memantine was not demonstrated in a large study involving patients with glaucoma. In a second phase III randomized, placebo-controlled trial involving over 2000 open angle glaucoma patients, including roughly 25% patients with NTG, oral memantine (10 or 20 mg daily) did not significantly delay glaucomatous visual field or optic nerve deterioration compared with placebo at 48-month follow up.63 Several biological and methodological factors may have contributed the failure of this study to meet its primary endpoint and replicate the results of its first phase III trial. While early enthusiasm for NMDA receptor blockade was largely driven by reports of markedly elevated levels of glutamate levels in vitreous samples of humans and animals with glaucoma64,65, these findings could not be replicated, weakening the premise of excitotoxicity as a dominant mechanism of RGC death.66,67 Moreover, NMDA receptors are expressed on multiple retinal cell types, which raised the question of why selective RGC loss would occur in glaucoma if global glutamatergic overactivation were the primary driver.68 Furthermore, the clinical trials relied on functional endpoints (standard automated perimetry [SAP], frequency doubling threshold) and a somewhat subjective structural endpoint (stereoscopic disc photography). This study also required discontinuation of the study drug once SAP progression was declared, which may have reduced the sensitivity to detect modest treatment effects over time with other endpoints.63 In a more recent animal study, investigators developed a novel memantine-nitrate derivative (MN-08) that combines NMDA receptor antagonism with nitric oxide-releasing properties.69 MN-08 demonstrated these dual therapeutic actions. It reduced apoptotic signaling to prevent RGC loss and ganglion cell complex (GCC) thinning, and also lowered intraocular pressure by promoting trabecular meshwork relaxation through nitric oxide and cyclic GMP-mediated pathways.69 Phase 1 trials of MN-08 are currently underway, although these are being conducted for pulmonary hypertension and not for glaucoma. Brimonidine Brimonidine is a commonly used glaucoma drug that acts as a selective alpha 2 adrenergic agonist to decrease aqueous production. Beyond brimonidine’s hypotensive effects, preclinical work suggests a potential neuroprotective role independent of IOP lowering. Experimental evidence suggests that brimonidine can reach the retinal tissues at therapeutic levels, bind to receptors on its target neurons, and activate intracellular pathways that increase neuronal resilience or prevent apoptosis.70 In addition to these direct neuronal effects, brimonidine has also been implicated in improving retinal vascular autoregulation. Because impaired blood flow and autoregulation are increasingly recognized as contributors to RGC vulnerability, modulation of ocular perfusion represents another promising avenue for protecting RGCs beyond IOP control. A non-randomized prospective study showed that brimonidine significantly enhanced

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Saini, Chhavi retinal vascular autoregulation.71 The authors hypothesized that the effects of brimonidine on retinal vascular autoregulation were likely due to its interactions with the nitric oxide signaling cascade.71,72 In a randomized, double masked clinical trial of patients with NTG, those treated with brimonidine 0.2% had significantly less visual field progression than those treated with timolol 0.5%, despite similar IOP control.73 Over a span of an average of 30 months, only 9% of brimonidine-treated patients progressed compared with 39% in the timolol group. This is despite higher average baseline IOP for patients completing the year 1 visit in the brimonidine group versus the timolol group (16.2 ±1.9 vs 15.3 ± 2.4 mmHg, p=0.031), suggesting a mechanism beyond IOP reduction. It should be noted that this study targeted patients with NTG where disease progression is more likely driven by non IOP-dependent mechanisms. However, these results have been questioned due to a large degree of patient dropout in the brimonidine group compared to timolol group due to ocular allergy symptoms (approximately 20% of the patients on brimonidine within 1 year of starting the medication). Nevertheless, this was the first large clinical trial in glaucoma patients to show the potential neuroprotective effect of a medication independent of IOP lowering. Nicotinamide Nicotinamide is a water-soluble vitamin and precursor for NAD+ and NADP, molecules essential for cellular energy regulation and multiple metabolic pathways.74 Studies in mouse models of glaucoma demonstrate that age-related declines in NAD+ and glutathione, alongside early mitochondrial abnormalities, render RGCs vulnerable to IOP-related stress.75 In animal models high-dose nicotinamide offered very significant neuroprotection, with up to 93% of treated mice eyes showing no optic nerve damage even at advanced stages of disease.75 In humans, a double-masked, randomized crossover trial of 57 glaucoma patients showed that high-dose supplementation of oral nicotinamide for 6 weeks (1.5 to 3 g/day) in addition to standard glaucoma therapy significantly improved inner retinal function compared with placebo.76 It is to be noted that this dosage of nicotinamide is 50 to 100 times of the recommended daily supplementation dose. At the 12 week mark, 27% (vs 16%) of the patients on nicotinamide showed visual field mean deviation improvement of ≥1 dB on nicotinamide and fewer deteriorating (4%) patients compared to placebo (12%), despite similar IOP (13.8 ± 4.1 mmHg in nicotinamide vs 13.4 ± 2.4 mmHg in placebo group).76 Similarly, in a separate phase 2 randomized, double-blind clinical trial, oral nicotinamide plus pyruvate was safe and produced short-term improvements in visual function measured by Humphery visual field (HVF) in patients with treated open-angle glaucoma at a median of 2.2 months.77 Several phase 3 trials aim to determine whether oral nicotinamide, when added to standard treatment, can slow vision loss in open angle glaucoma patients.78 However, a recent report from a phase 2/3 trial described a case of drug-induced liver injury likely related to high-dose nicotinamide (3 g/day), which is a known toxicity.79,80 Hence, the investigators suggested that the clinical benefit and safety of high-dose nicotinamide supplementation for glaucoma need to be further studied before it is used clinically in glaucoma patients.

Potential Treatments Focusing on Neuroenhancement Trabeculectomy Evidence suggests that dramatic lowering of IOP with trabeculectomy not only slows glaucomatous progression but may partly restore retinal ganglion cell function. The Collaborative Initial Glaucoma Treatment Study (CIGTS), a randomized trial comparing trabeculectomy with medical therapy for newlydiagnosed patients with open angle glaucoma, showed both groups developed similar rates of visual field loss after eight years.81 However, some patients in the trabeculectomy group exhibited reversal of cupping compared to the medical group.82 At five year follow up, significantly more surgically-treated eyes showed improvement in pattern standard deviation (30% vs 7%, P = 0.02), suggesting a true biological effect beyond structural restoration. Importantly, these functional improvements corresponded to substantially better IOP control in the surgical group (9.9 ± 4.7 mmHg vs 18.0 ± 6.7 mmHg baseline), whereas eyes treated with medication alone showed no meaningful IOP change (13.7 ± 3.2 mmHg vs 13.7 ± 2.6 mmHg, P = .92).83 Caprioli et al. reported that in a retrospective, comparative, longitudinal cohort study, trabeculectomy can improve visual function long-term. In the trabeculectomy group, the proportion of VF point locations with improved sensitivity after surgery were significantly higher than those in a matched, unoperated comparison

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2026 Harvard Ophthalmology Residents’ Course group.84 It is noteworthy, however, that the surgical cohort had a relatively low preoperative IOP (mean 15 mm Hg), achieving only a modest additional reduction of approximately 30% postoperatively (mean 10 mm Hg), suggesting that even small decreases in IOP or a decrease in IOP fluctuation may be sufficient to restore function in a subset of metabolically compromised but still viable RGCs.84 This potential for functional recovery in glaucoma following trabeculectomy is also reflected in clinical practice. We recently cared for a patient with mixed mechanism glaucoma and progressive visual field loss despite consistently low IOPs (8-10 mmHg) and a prior Ahmed glaucoma valve implantation. The patient had thin corneas, a history of disc hemorrhage, and visual fields demonstrating steady deterioration over several years, with mean deviation worsening from approximately -13 dB to -22 dB despite excellent IOP control and adherence to medical therapy (Figure 3). Given continued progression, a trabeculectomy was performed. Postoperatively, the patient reported clearer vision, her visual acuity improved, and most importantly, visual fields showed meaningful functional recovery, with mean deviation improving from -22 dB preoperatively to -20 dB at post operative year 1 and later to -16 dB at postoperative year 2 despite IOP similar to those measured preoperatively. This case also illustrates that even in eyes with low preoperative IOP and advanced disease, trabeculectomy can relieve sufficient biomechanical and metabolic stress likely related to IOP fluctuation to reverse RGC dysfunction and produce measurable and clinically meaningful improvement in visual function. However, it should be noted that trabeculectomy is not an ideal solution for many patients. The procedure carries notable risks including hypotony, bleb-related infection, choroidal effusions, and cataract progression that limits its applicability.85,86 In addition, long term success is often compromised by subconjunctival fibrosis and bleb failure. NT-501 CNTF Implant A ciliary neurotrophic factor (CNTF) implant (NT-501) is an encapsulated cell therapy device that continuously releases CNTF into the vitreous cavity for months to years from genetically engineered cells and is designed to provide sustained neurotrophic support to RGCs.87 Experimental glaucoma models have shown that administration of CNTF enhances RGC survival and axonal regeneration, supporting its potential as a neuroprotective strategy.88 In a phase I trial of 11 POAG patients, the high-dose CNTFsecreting NT-501 implant was safe and well tolerated, and implanted eyes showed signs of both structural and functional improvements.89 The most common adverse effect was miosis.89,90 These findings have led to two ongoing randomized sham-controlled masked phase II studies designed to more rigorously evaluate efficacy, including a 60 participant trial comparing a single NT-501 implant to sham over 24 months in POAG, and a dual implant trial randomizing eyes to receive two NT-501 implants vs sham.89 Together, these studies will determine whether sustained CNTF delivery via encapsulated cell technology can provide clinically meaningful neuroprotection and/ or neuroenhancement in glaucoma. Topically Administered Insulin Insulin is a peptide hormone whose signaling is initiated by binding to a transmembrane insulin receptor. Once activated, these receptors engage pathways like phosphoinositide-3 kinase (PI3K)/protein kinase B (Akt) pathways in retinal neuronal, glial, and vascular cells, influencing several pathways that are known to be dysregulated in glaucoma.91,92 Restoring insulin signaling in these cells may therefore offer therapeutic benefit. Intranasal administration of insulin, which allows insulin to directly reach the CNS, bypassing the blood-brain barrier and avoiding changes in peripheral glucose, has shown promising effects in experimental models of neurodegenerative diseases, such as Alzheimer’s and Parkinson’s disease.93,94 Furthermore, in mouse models of retinal injury, insulin has also been shown to promote regeneration of RGC dendritic processes and rescue light-triggered retinal responses by potentially reversing injuryinduced reduction in mammalian target of rapamycin (mTOR) signaling, a central regulator of cell metabolism and cell survival.95 More recently a phase I clinical trial has evaluated topical recombinant human insulin in patients with glaucoma.96 Participants received either low (4 units/drop) or high (20 units/drop) dose insulin daily for five days in clinic or self-administered for 28 days. Notably, in the month following treatment, five of 15 treated study eyes demonstrated significant increase in RNFL thickness (≥5 µm), accompanied by corresponding GCC thickening compared to controls.96 Overall, the treatment was safe and well tolerated with no serious adverse events and no systemic alterations in glucose, electrolytes,

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Saini, Chhavi or HbA1c. Future work and larger studies will be needed to see if these structural improvements are accompanied by functional improvements for patients with glaucoma.

Early Treatments Targeting Neuroinflammation ANX007 (Anti-C1q) Prior work has identified deficiency in intrinsic regulation of complement activation in glaucoma. In particular, C1q, the initiating molecule of the classical complement pathway, is found in abundance in both animal glaucoma models and retina of glaucoma patients.97,98 C1q is produced by both local microglia and by infiltrating immune cells99,100 and is one of the activating molecules that can lead to proinflammatory A1 astrocytes.41 Furthermore, loss of C1qa significantly protected RGCs in a murine model of retinal ischemia.101 ANX007 is a monoclonal antibody Fab that selectively binds C1q substrate binding sites to prevent activation of the classical complement pathway.99 In primate models, intravitreal injection of ANX007 correlated with inhibition of free C1q in ocular fluids and retinal tissue, demonstrating robust target engagement.102 Following these preclinical trials, Sun and colleagues have reported safety, tolerability and full target engagement after intravitreal injection of ANX007 in 26 POAG patients.103 While future work will be needed to determine if ANX007 may lead to structural and functional improvements in glaucoma patients, this compound is undergoing active clinical evaluation in age-related macular degeneration (NCT06510816). GLP-1 Agonists Human glucagon-like peptide-1 (GLP-1) analogues have been used for the clinical care of patients with diabetes and have shown benefits in terms of cardiovascular risk reduction.104,105 GLP-1 receptors have been detected in a small fraction of neurons in the ganglion cell layer.106 In a hypertensive glaucoma mouse model, GLP-1 receptor agonists (GLP-1Ra) administered both topically and systemically preserved RGCs, reduced microglia/macrophage activation, and prevented A1 transcriptional changes in astrocytes and Müller glia.107 In addition to these preclinical findings, a large retrospective insurance claims study of approximately 2000 new GLP-1Ra users found that exposure to this drug class was associated with a 44% lower hazard of developing glaucoma compared with matched diabetic controls, supporting a potential protective effect in humans.108 A recent systematic review and meta-analysis evaluated whether GLP-1R agonists reduce glaucoma incidence in patients with type 2 diabetes.109 However, pooled analysis showed no statistically significant difference in glaucoma incidence between GLP-1Ra users and non-users (HR 0.78, 95% CI 0.59-11.04), with substantial heterogeneity. Yet sensitivity analyses revealed that exclusion of one study whose control group was dominated by Sodium-Glucose Cotransporter 2 (SGLT-2) inhibitor users changed the conclusion, whereby GLP-1Ra use was associated with a significant 29% risk reduction (HR 0.71, 95% CI 0.60-0.85) and markedly reduced heterogeneity.109 Importantly, a recent retrospective matched cohort study from Massachusetts Eye and Ear reported an increased risk of nonarteritic anterior ischemic optic neuropathy among patients prescribed semaglutide.110 While observational and not causal, this finding underscores the need for prospective safety studies before GLP-1R agonists can be considered as neuroprotective therapies in glaucoma.

Challenges and Future Trial Design The first major clinical trial evaluating neuroprotective effect of memantine in glaucoma demonstrated how difficult it is to translate preclinical data into clinical success. The study ultimately failed to meet its endpoints after an investment estimated at 80 million dollars over seven years.63 The trial highlighted several key limitations in designing these types of studies, including broad patient eligibility, slow rates of visual field progression in glaucoma, and reliance on stringent event-based functional outcomes without parallel objective and quantitative structural or molecular markers. Looking ahead, several strategies may improve our ability to detect meaningful neuroprotective effects in glaucoma (Table 1). Including patients who progress more quickly or who show biological signatures of increased vulnerability may increase the likelihood of capturing treatment effects. Incorporating emerging

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2026 Harvard Ophthalmology Residents’ Course biomarkers of neurodegeneration and neuroinflammation may also be helpful, such as aqueous humor neurofilament light chain, APOE and Galectin 3, and potentially systemic cytokines of immune dysregulation.33,111,112 Adaptive inflammatory markers, including those specific to HSP-specific Th1 responses, reduced regulatory T cell activity, and proinflammatory cytokine profiles including IFN-γ and TNF-α, could also be used to identify these patients.48 Therapeutic candidates should ideally target validated disease pathways and there should be sustained intraocular delivery platforms to ensure consistent target engagement. Advances in outcome measures are also critical. Since the memantine trial, more objective structural endpoints and functional endpoints with better sensitivity have been developed in glaucoma. Trend-based OCT analyses with RNFL thickness and GCC measurements, which provide quantitative reliable measurements of RGCs and their axons, may prove beneficial. Functional testing strategies can also be optimized. For instance, clustering visual field assessments at baseline and at predefined follow-up intervals has been shown to improve the detection of rapid visual field progressionClick or tap here to enter text..113 Furthermore, novel imaging modalities such as detection of apoptotic retinal cells (DARC) or flavoprotein fluorescence, which helps visualize RGC apoptosis in vivo and mitochondrial oxidative stress in the retina, respectively, may provide more sensitive outcomes than visual fields alone.114–117 Integration of immune biomarkers with structural and functional outcomes may also prove beneficial. Finally, timely and transparent reporting of negative as well as positive results is essential. Early dissemination of results, even if negative, can help refine hypotheses and improve future trial design. Together, these approaches provide a more biologically informed roadmap for the next generation of glaucoma neuroprotection and neuroenhancement studies, which are aimed to develop treatments for glaucoma beyond IOP control.

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2026 Harvard Ophthalmology Residents’ Course 64. Brooks DE, Garcia GA, Dreyer EB, Zurakowski D, Franco-Bourland RE. Vitreous body glutamate concentration in dogs with glaucoma. Am J Vet Res. 1997;58(8):864-867. 65. Dreyer EB, Zurakowski D, Schumer RA, Podos SM, Lipton SA. Elevated glutamate levels in the vitreous body of humans and monkeys with glaucoma. Arch Ophthalmol. 1996;114(3):299-305. 66. Levkovitch-Verbin H, Martin KRG, Quigley HA, Baumrind LA, Pease ME, Valenta D. Measurement of amino acid levels in the vitreous humor of rats after chronic intraocular pressure elevation or optic nerve transection. J Glaucoma. 2002;11(5):396-405. 67. Wamsley S, Gabelt BT, Dahl DB, et al. Vitreous glutamate concentration and axon loss in monkeys with experimental glaucoma. Arch Ophthalmol. 2005;123(1):64-70. 68. Osborne NN. Recent clinical findings with memantine should not mean that the idea of neuroprotection in glaucoma is abandoned. Acta Ophthalmol. 2009;87(4):450-454. 69. Hu H, Wu L, Hu X, et al. Neuroprotective and intraocular pressure lowering effects of dual-functional memantine nitrate MN-08 on the experimental models of glaucoma. Scientific Reports 2025 15:1. 2025;15(1):23822-. 70. Saylor M, McLoon LK, Harrison AR, Lee MS. Experimental and clinical evidence for brimonidine as an optic nerve and retinal neuroprotective agent: an evidence-based review. Arch Ophthalmol. 2009;127(4):402-406. 71. Feke GT, Bex PJ, Taylor CP, et al. Effect of brimonidine on retinal vascular autoregulation and short-term visual function in normal tension glaucoma. Am J Ophthalmol. 2014;158(1). 72. Hein TW, Rosa RH, Yuan Z, Roberts E, Kuo L. Divergent Roles of Nitric Oxide and Rho Kinase in Vasomotor Regulation of Human Retinal Arterioles. Invest Ophthalmol Vis Sci. 2010;51(3):1583-1590. 73. Krupin T, Liebmann JM, Greenfield DS, Ritch R, Gardiner S. A randomized trial of brimonidine versus timolol in preserving visual function: Results from the low-pressure glaucoma treatment study. Am J Ophthalmol. 2011;151(4):671-681. 74. Rennie G, Chen AC, Dhillon H, Vardy J, Damian DL. Nicotinamide and neurocognitive function. Nutr Neurosci. 2015;18(5):193-200. 75. Williams PA, Harder JM, Foxworth NE, et al. Vitamin B3 modulates mitochondrial vulnerability and prevents glaucoma in aged mice. Science. 2017;355(6326):756-760. 76. Hui F, Tang J, Williams PA, et al. Improvement in inner retinal function in glaucoma with nicotinamide (vitamin B3) supplementation: A crossover randomized clinical trial. Clin Exp Ophthalmol. 2020;48(7):903-914. 77. De Moraes CG, John SWM, Williams PA, Blumberg DM, Cioffi GA, Liebmann JM. Nicotinamide and Pyruvate for Neuroenhancement in Open-Angle Glaucoma: A Phase 2 Randomized Clinical Trial. JAMA Ophthalmol. 2021;140(1):11. 78. Nicotinamide in Glaucoma (NAMinG): a Randomised, Placebo-controlled, Multi-centre, Phase III Trial | Cochrane Library. Accessed December 4, 2025. https://www.cochranelibrary.com/central/doi/10.1002/central/CN02405727/full 79. Shukla AG, Cioffi GA, Liebmann JM. Drug-Induced Liver Injury During a Glaucoma Neuroprotection Clinical Trial. J Glaucoma. 2024;33(8):e58-e59. 80. Winter SL, Boyer JL. Hepatic Toxicity from Large Doses of Vitamin B 3 (Nicotinamide) . New England Journal of Medicine. 1973;289(22):1180-1182. 81. Musch DC, Gillespie BW, Lichter PR, Niziol LM, Janz NK. Visual Field Progression in the Collaborative Initial Glaucoma Treatment Study: The Impact of Treatment and other Baseline Factors. Ophthalmology. 2008;116(2):200. 82. Parrish RK, Feuer WJ, Schiffman JC, Lichter PR, Musch DC. Five-year follow-up optic disc findings of the Collaborative Initial Glaucoma Treatment Study. Am J Ophthalmol. 2009;147(4):717. 83. Wright TM, Goharian I, Gardiner SK, Sehi M, Greenfield DS. Short-term enhancement of visual field sensitivity in glaucomatous eyes following surgical intraocular pressure reduction. Am J Ophthalmol. 2015;159(2):378-385.e1.

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Saini, Chhavi 84. Caprioli J, De Leon JM, Azarbod P, et al. Trabeculectomy Can Improve Long-Term Visual Function in Glaucoma. Ophthalmology. 2016;123(1):117-128. 85. Gedde SJ, Chen PP, Heuer DK, et al. The Primary Tube Versus Trabeculectomy (PTVT) Study: Methodology of a Multicenter Randomized Clinical Trial Comparing Tube Shunt Surgery and Trabeculectomy with Mitomycin C. Ophthalmology. 2017;125(5):774. 86. Gedde SJ, Schiffman JC, Feuer WJ, Herndon LW, Brandt JD, Budenz DL. Treatment outcomes in the tube versus trabeculectomy (TVT) study after five years of follow-up. Am J Ophthalmol. 2012;153(5):803.e2. 87. Thanos CG, Bell WJ, O’Rourke P, et al. Sustained secretion of ciliary neurotrophic factor to the vitreous, using the encapsulated cell therapy-based NT-501 intraocular device. Tissue Eng. 2004;10(11-12):1617-1622. 88. Hu Y, Grodzki LM, Bartsch U. Survival and Axonal Regeneration of Retinal Ganglion Cells in a Mouse Optic Nerve Crush Model After a Cell-Based Intravitreal Co-Administration of Ciliary Neurotrophic Factor and Glial Cell LineDerived Neurotrophic Factor at Different Post-Lesion Time P…. Cells. 2025;14(9):643. 89. Goldberg JL, Beykin G, Satterfield KR, Nuñez M, Lam BL, Albini TA. Phase I NT-501 Ciliary Neurotrophic Factor Implant Trial for Primary Open-Angle Glaucoma: Safety, Neuroprotection, and Neuroenhancement. Ophthalmology Science. 2023;3(3):100298. 90. Chew EY, Clemons TE, Peto T, et al. Ciliary neurotrophic factor for macular telangiectasia type 2: Results from a phase 1 safety trial. Am J Ophthalmol. 2015;159(4):659-666.e1. 91. Chiu SL, Cline HT. Insulin receptor signaling in the development of neuronal structure and function. Neural Dev. 2010;5(1):7. 92. Niswender KD, Morrison CD, Clegg DJ, et al. Insulin activation of phosphatidylinositol 3-kinase in the hypothalamic arcuate nucleus: a key mediator of insulin-induced anorexia. Diabetes. 2003;52(2):227-231. 93. Pang Y, Lin S, Wright C, et al. Intranasal insulin protects against substantia nigra dopaminergic neuronal loss and alleviates motor deficits induced by 6-OHDA in rats. Neuroscience. 2016;318:157. 94. Guo Z, Chen Y, Mao YF, et al. Long-term treatment with intranasal insulin ameliorates cognitive impairment, tau hyperphosphorylation, and microglial activation in a streptozotocin-induced Alzheimer’s rat model. Sci Rep. 2017;7:45971. 95. Agostinone J, Alarcon-Martinez L, Gamlin C, Yu WQ, Wong ROL, Di Polo A. Insulin signalling promotes dendrite and synapse regeneration and restores circuit function after axonal injury. Brain. 2018;141(7):1963. 96. Smith ZW, Beykin G, Saludares M, et al. A Phase 1 Trial of Topical Insulin for Patients with Glaucoma. Invest Ophthalmol Vis Sci. 2024;65(7):668-668. 97. Tezel G, Yang X, Luo C, et al. Oxidative Stress and the Regulation of Complement Activation in Human Glaucoma. Invest Ophthalmol Vis Sci. 2010;51(10):5071-5082. 98. Stasi K, Nagel D, Yang X, et al. Complement Component 1Q (C1Q) Upregulation in Retina of Murine, Primate, and Human Glaucomatous Eyes. Invest Ophthalmol Vis Sci. 2006;47(3):1024-1029. 99. Jiao H, Rutar M, Fernando N, et al. Subretinal macrophages produce classical complement activator C1q leading to the progression of focal retinal degeneration. Molecular Neurodegeneration 2018 13:1. 2018;13(1):45-. 100. Katschke KJ, Xi H, Cox C, et al. Classical and alternative complement activation on photoreceptor outer segments drives monocyte-dependent retinal atrophy. Scientific Reports 2018 8:1. 2018;8(1):7348-. 101. Silverman SM, Kim BJ, Howell GR, et al. C1q propagates microglial activation and neurodegeneration in the visual axis following retinal ischemia/reperfusion injury. Mol Neurodegener. 2016;11(1):24. 102. Grover A, Sankaranarayanan S, Mathur V, et al. Pharmacokinetic and Target Engagement Measures of ANX007, an Anti-C1q Antibody Fragment, Following Intravitreal Administration in Nonhuman Primates. Invest Ophthalmol Vis Sci. 2023;64(2):3. 103. Sun Y, Wirta D, Murahashi W, et al. Safety and Target Engagement of Complement C1q Inhibitor ANX007 in Neurodegenerative Eye Disease: Results from Phase I Studies in Glaucoma. Ophthalmology Science. 2023;3(2):100290.

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2026 Harvard Ophthalmology Residents’ Course 104. Marso SP, Bain SC, Consoli A, et al. Semaglutide and Cardiovascular Outcomes in Patients with Type 2 Diabetes. N Engl J Med. 2016;375(19):1834-1844. 105. Pratley RE, Aroda VR, Lingvay I, et al. Semaglutide versus dulaglutide once weekly in patients with type 2 diabetes (SUSTAIN 7): a randomised, open-label, phase 3b trial. Lancet Diabetes Endocrinol. 2018;6(4):275-286. 106. Hebsgaard JB, Pyke C, Yildirim E, Knudsen LB, Heegaard S, Kvist PH. Glucagon-like peptide-1 receptor expression in the human eye. Diabetes Obes Metab. 2018;20(9):2304-2308. 107. Lawrence ECN, Guo M, Schwartz TD, et al. Topical and systemic GLP-1R agonist administration both rescue retinal ganglion cells in hypertensive glaucoma. Front Cell Neurosci. 2023;17:1156829. 108. Sterling J, Hua P, Dunaief JL, Cui QN, VanderBeek BL. Glucagon-like peptide 1 receptor agonist use is associated with reduced risk for glaucoma. Br J Ophthalmol. 2023;107(2):215-220. 109. Amaral DC, Guedes J, Cruz MRB, et al. GLP-1 Receptor Agonists Use and Incidence of Glaucoma: A Systematic Review and Meta-Analysis. Am J Ophthalmol. 2025;271:488-497. 110. Hathaway JT, Shah MP, Hathaway DB, et al. Risk of Nonarteritic Anterior Ischemic Optic Neuropathy in Patients Prescribed Semaglutide. JAMA Ophthalmol. 2024;142(8):732-739. 111. Lin JB, Pitts KM, Helwe H El, et al. Neurofilament Light Chain in Aqueous Humor as a Marker of Neurodegeneration in Glaucoma. Clin Ophthalmol. 2023;17:2209-2217. 112. Lin JB, El Helwe H, Falah H, et al. Evaluation of Serum and Aqueous Humor Neurofilament Light Chain as Markers of Neurodegeneration in Glaucoma. Transl Vis Sci Technol. 2025;14(2):24-24. 113. Medeiros FA, Malek DA, Tseng H, et al. Short-term Detection of Fast Progressors in Glaucoma: The Fast Progression Assessment through Clustered Evaluation (Fast-PACE) Study. Ophthalmology. 2024;131(6):645-657. 114. Cordeiro MF. DARC: a new method for detecting progressive neuronal death. Eye 2007 21:1. 2007;21(1):S15-S17. 115. Ahsanuddin S, Rios HA, Otero-Marquez O, et al. Flavoprotein fluorescence elevation is a marker of mitochondrial oxidative stress in patients with retinal disease. Frontiers in Ophthalmology. 2023;3:1110501. 116. Zhou DB, Castanos M V., Geyman L, et al. Mitochondrial Dysfunction in Primary Open-Angle Glaucoma Characterized by Flavoprotein Fluorescence at the Optic Nerve Head. Ophthalmol Glaucoma. 2022;5(4):413-420. 117. Cordeiro MF, Hill D, Patel R, Corazza P, Maddison J, Younis S. Detecting retinal cell stress and apoptosis with DARC: Progression from lab to clinic. Prog Retin Eye Res. 2022

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Floppy Eyelid Syndrome: A Review of Diagnosis, Associations, and Management Hueyjong Shih, MD; and Michael K. Yoon, MD

Introduction Floppy eyelid syndrome (FES) is an ophthalmic condition that was first described by Culbertson and Ostler in 1981 in a group of 11 overweight men with rubbery upper eyelids and refractory upper eyelid papillary conjunctivitis.1 Common symptoms of FES include irritation, foreign body sensation, redness, and mucoid discharge. During sleep, the eyelids of patients with FES are thought to spontaneously evert due to traction against the sleeping surface (such as a pillow), contributing to the papillary response of the upper tarsus.1 The goal of this article is to provide an up-to-date overview on the assessment and diagnosis of floppy eyelid syndrome, summarize associations that have been discovered with other medical conditions, and identify current treatments and treatment outcomes for patients with FES.

Symptoms and Associations Patients with FES present with a wide range of nonspecific symptoms including chronic ocular irritation, foreign body sensation, redness, and mucous discharge.2 These symptoms are often misdiagnosed as other common ocular conditions, such as blepharitis or dry eye syndrome. Due to eyelid eversion during sleep, there is often a chronic papillary conjunctival change as well as corneal changes in patients with FES.3 Eyelid abnormalities associated with FES include blepharochalasis (nonpitting edema of the upper eyelids), ptosis, lash ptosis, lash disorganization (loss of lash parallelism), trichiasis, upper and lower lid entropion, and skin changes (increased fine wrinkles).4–6 Corneal findings of FES include punctate surface keratopathy and keratoconus. Patients with FES were also found to have lower corneal hysteresis values compared to patients without FES.7

Assessment and Diagnosis Clinical examination and diagnosis of FES begins with manipulation of the upper eyelids. The examiner should distract the upper eyelid superiorly and laterally with attention focused on the laxity of the upper eyelid and tarsus, the resistance felt when the eyelid is distracted, and the presence or absence of spontaneous eyelid eversion. Over the years, there have been multiple measurement tests devised to quantify eyelid laxity in a more objective manner. These can be categorized with regards to the direction the eyelid is distracted during the test. The McNab vertical lid pull / distraction test was suggested in 1997 and involves pulling the upper lid upwards by placing a finger over the tarsal plate, and measuring the vertical excursion of the lid margin.8 FES patients were found to fall into the range of 15-25mm for the upper lid compared to a 5-10mm in a control group of age- and sex- matched patients.8 Another measurement which involves vertical eyelid distraction is the “upper eyelid distraction distance (UEDA)” which is the distance from the posterior margin of the upper lid to the bulbar conjunctiva when the patient looks in downgaze.9,10 In a study of 262 patients ≥55 years old, this measurement was found to be statistically different between the eyelid of the side the patient slept on (mean: 6.060mm) compared to the side the patient did not sleep on (mean: 4.859mm). An anterior distraction test has also been suggested in which the lids are drawn anterior to the cornea by the eyelashes, and the distance between the anterior corneal pole and the distracted eyelid margin is measured using a transparent ruler.11 This measurement was found to be significantly different in 11 patients with unilateral FES in the affected (mean: 17.09mm) compared to unaffected (mean: 11.72mm) eyes.11 Finally, Karger et al. devised a method to measure eyelid laxity by securing a gold weight attached to a strain gauge to the pretarsal upper eyelid skin using medical adhesive tape, and applying upward traction through the strain gauge until the lid was displaced 5mm. This study found that the mean force required to displace the eyelid was correlated to subjective ease of lid eversion.12 Although these methods have been published, there is no “gold standard” or consensus measurement used to define floppy eyelid syndrome, and diagnosis is often still made clinically with superior and lateral upper eyelid distraction.

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Figure 1: Eyelid Distraction Test to identify Floppy Eyelid Syndrome External photographs of two patients with their eyelids distracted superiorly and laterally.

In both patients, the left upper eyelid displays evidence of spontaneous eversion and significant laxity. Figure 2: Lash Ptosis

External photographs of two patients in primary gaze. In both patients, the left upper eyelid with suspected floppy eyelid syndrome exhibits evidence of lash ptosis (downward angling of the eyelashes). The left upper eyelids of both patients also exhibit blepharoptosis, as evidenced by a decreased marginal reflex distance 1 (MRD1), the distance between the corneal light reflex to the central upper eyelid margin. Figure 3: Lash Disorganization and Skin Changes

External photographs of two patients in down gaze. In both patients, the left upper eyelid with suspected floppy eyelid syndrome exhibits evidence of lash disorganization (loss of parallelism), as well as skin changes such as an increase in fine wrinkles and telangiectasias.

Association with Obstructive Sleep Apnea and other Conditions The association between FES and obstructive sleep apnea (OSA) was first suggested in 1990 by a case series of 3 patients with floppy eyelid syndrome and obstructive sleep apnea, after anecdotal reports that patients who presented with floppy eyelid syndrome were overweight males with a habitus characteristic of OSA.13

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Shih, Hueyjong OSA is a condition characterized by partial or complete upper airway obstruction during sleep, associated with oxygen desaturation and re-saturation sequences.14 Patients with OSA often snore and exhibit other symptoms, including excessive daytime sleepiness, fatigue, and low motivation despite getting adequate amounts of sleep.15 Screening for sleep apnea includes a detailed sleep history, as well as physical features such as a large neck circumference, elevated BMI, or a Friedman class tongue position of 3 or greater (where only the soft palate and base of uvula are visible when the mouth is wide open).15 There have also been questionnaires developed (such as STOP-Bang) which have a high sensitivity and specificity to detect moderate and severe sleep apnea, although polysomnography is the gold standard of evaluation for OSA.16 Diagnostic guidelines for OSA based on polysomnography findings were published by the American College of Physicians in 2014.17 Identification of patients who have OSA is important because it has been shown to be associated with increased risk of cardiovascular and cerebrovascular events, coronary artery disease, and stroke.14 Treatment of OSA includes positive airway pressure to maintain upper airway patency and prevent collapse, mandibular advancement devices which protrude the mandible and open the airway by pulling the base of the tongue forward, and the hypoglossal nerve stimulator, which stimulates the hypoglossal nerve to bring the base of the tongue forward in order to open the airway.18 When the association between OSA and FES was first identified, OSA was thought to be caused by abnormal laxity of the oropharyngeal tissues, and it was hypothesized that similar structural abnormalities in the tarsal plate or canthal tendons played a role in the development of FES.13 Since then, several meta-analyses have been conducted on studies investigating this association.14,19–22 Prior to these metaanalyses, the prevalence of FES in patients with OSA reported in literature varied considerably.23 Two separate studies, in 1999 and 2006, investigating patients referred for suspected sleep apnea, found a prevalence of FES in OSA patients of 34% and 2%, respectively, although these studies were limited by small sample sizes (44 OSA patients in each study).12,24 The prevalence of FES or eyelid laxity in patients with OSA has been estimated to be as high as 50% in a 2017 study investigating 296 patients with OSA. This study defined eyelid laxity defined as a horizontal distraction > 5mm for the upper eyelid, and FES as both the presence of an easy eversion sign of the upper eyelid and the presence of large papillae in the same eyelid conjunctiva.25 Subsequent meta-analyses have generally agreed that there is a positive association between OSA and FES, with statistically significant odds ratios of FES in patients with OSA ranging from 1.89 to 4.17.14 These meta-analyses each analyzed greater than 5 studies with a total population of over 700 total patients.14,21,22 Furthermore, in sub-group analysis stratified by OSA severity, two of the meta-analyses agreed that increasing severity of OSA correlated with increased risk of FES.21,22 The limitations of these meta-analyses include a significant selection bias; many of the included studies were performed in patients who presented to clinic to evaluate for OSA, and may not be representative of the entire OSA population, many of whom remain undiagnosed. Control patients in these studies also may not be representative of the non-OSA population, given that they were under consideration for potential OSA symptoms. Another significant limitation of these meta-analyses is the lack of adjustment for important confounders, such as age, gender, and body mass index, each of which may independently be associated with both FES and obstructive sleep apnea. Other meta-analyses have investigated the prevalence of OSA in patients diagnosed with FES. One study included 12 reports comprising 511 patients and found that the prevalence of OSA is 57% in people with FES, compared to 2-5% in the general population.19 Furthermore, FES was found to be associated with certain ocular comorbidities, including tear film abnormalities, keratoconus, glaucoma, and lower eyelid entropion.19 Systemic comorbidities associated with FES included obesity (defined as BMI > 30kg/m2), systemic hypertension, and diabetes.19

Treatment and Treatment Outcomes Treatment of FES ranges from conservative to surgical. Conservative management, including ocular surface lubrication with lubricant eyedrops or gels, aims to treat many of the sequelae related to the easily everted upper eyelid, such as punctate epithelial keratopathy, corneal vascularization, and keratoconus.26,27 Eyelid taping combined with nighttime ointment has been shown to be an effective

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2026 Harvard Ophthalmology Residents’ Course method to prevent ocular surface disorders in ICU patients who lose the ability to protect the ocular surface, and is occasionally recommended for FES as well.28 Given the link between FES and OSA, OSA treatment has been investigated as a possible way to manage FES. One study of 47 patients with newly diagnosed OSA revealed that 34% of patients had concurrent FES, and after treatment with 6 months of CPAP therapy, FES resolved in 53.8% of patients.29 This effect was hypothesized to due to CPAP’s ability to reverse laryngeal collapse, thereby halting systemic hypoventilation, improving oxygenation of eyelid connective tissue, and restoring tarsal integrity. Patients with non-reversible FES were found to have more severe OSA in this study.29 Surgical treatments of FES aim to restore normal eyelid function by tightening the upper eyelid; these include the lateral tarsal strip, medial canthoplasty, full-thickness wedge resection, upper eyelid blepharoplasty, and canthal suspension procedures.30–32 Studies investigating surgical outcomes from these procedures report an overall high patient satisfaction and symptom reduction rate.4,26 In 1985, Dr. Jonathan Dutton described success of a full-thickness resection of the lateral one-third to one-half of the eyelid, performed with primary layered closure in five eyes of four patients with floppy eyelid syndrome.31 All patients experienced improvement of symptoms, including chronic discharge, redness, irritation, pain, and burning.31 Objective measurements of FES-associated eyelid changes also show improvement after surgical procedures. A 2007 study of 24 eyelids that underwent standard full-thickness pentagonal wedge resection for clinically diagnosed FES demonstrated a statistically significant difference between preoperative and postoperative margin reflex distance (MRD).33 More recently, in a 2024 study of around 30 eyes comparing conservative and full thickness wedge resection surgery in patients with floppy eyelids, patients who underwent surgical treatment had significantly increased tear break up time, lower fluorescein staining and ocular surface disease index scores, and improvement in corneal in vivo confocal microscopy findings, including dendritic cell count, nerve tortuosity, and nerve density, compared to those undergoing conservative treatment.34

Surgical Complications and Sequelae However, there are also reports which describe challenging surgical complications or outcomes in patients with floppy eyelid syndrome. A recent case report describes two patients with floppy eyelid syndrome who underwent levator aponeurosis advancement and presented with severe foreign body sensation in the weeks to months following their procedure.35 Upon examination of the everted upper eyelid, a kinked, “taco shell” deformity configuration of the tarsus was found in both patients, which the authors hypothesized was due to the floppy tarsus buckling with upward traction due to insertion of the levator aponeurosis on the anterior tarsal surface.35 Similarly, a 43-year-old woman who underwent wedge excision of the medial and lateral upper eyelid for FES, followed by a ptosis repair three months later, was found to have conjunctiva folding below the upper eyelid margin, which progressed to fornix prolapse and obliteration down to the limbus of the upper eyelid.36 Again, the authors hypothesized that abnormal eyelid anatomy was responsible for the complication, theorizing that suspensory ligaments in the fornices had degraded similarly to the tarsal elastin, or that advancement of the levator muscle could have pulled the suspensory ligaments inferiory.36 Perhaps unsurprisingly, this difficulty in achieving a satisfactory surgical eyelid outcome has also been reported in patients with OSA. A study of over 577 patients who underwent ptosis repair, either by levator advancement or Müller muscle-conjunctiva resection, showed a statistically significant difference in surgical failure between patients with OSA and those without (20.5% vs 13.1%).37

Conclusion FES is an ophthalmic condition, initially identified in overweight patients, that presents with easily everted eyelids coupled with foreign body sensation, mucous discharge, and, in some instances, corneal pathology. Although many methods have been devised to objectively define this condition, it is still mainly a clinical diagnosis. Recently, several meta-analyses have suggested an increased risk of FES in patients with OSA. These studies, however, are limited by selection bias and lack of adjustment for confounding variables such as age, BMI, and gender. Although surgical techniques to tighten the upper eyelid result in improvement in patient symptoms and objective eyelid and corneal measurements, there are reported

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Shih, Hueyjong complications which can arise from routine eyelid surgeries given the altered anatomy in patients with FES. Future studies should continue to investigate the pathophysiology behind differences in eyelid elasticity in FES patients and refine surgical techniques to improve outcomes accordingly.

FIGURE 1: Routes of gene therapy administration Depiction of current routes of administration for intraocular gene therapies. A. Subretinal injection following pars plana vitrectomy. B. Intravitreal injection. C. Suprachoroidal injection.

FIGURE 2: Nonviral vectors for gene therapy delivery A. Lipid nanoparticle-based vectors encapsulating genetic material, with the outer shell demonstrating PEGylated lipids and cholesterol molecules. B. Polymer-based vectors demonstrating a “spaghetti-andmeatballs” configuration for delivery of genetic material.

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2026 Harvard Ophthalmology Residents’ Course

Hereditary Optic Neuropathies: Clinical Characteristics, Pathophysiology, and Novel Therapeutic Approaches Moosa H. Zaidi, MD; and Ryan Gise, MD

Abstract Hereditary optic neuropathies (HONs) comprise genetically diverse disorders of progressive degeneration of retinal ganglion cells (RGCs) and their axons, resulting in optic atrophy and eventually often severe visual dysfunction. Specific underlying mechanisms vary and include endoplasmic reticulum stress, altered mitochondrial dynamics, and impaired oxidative phosphorylation. However, most share a pathophysiology involving the selective vulnerability of highly metabolically active RGCs. The two primary inherited optic neuropathies are Leber hereditary optic neuropathy (LHON) and autosomal dominant optic atrophy (DOA). However, the full spectrum of inherited disorders that include optic neuropathy as a feature is broad and comprises disorders with varied inheritance, epidemiology, and clinical characteristics. Currently idebenone, a synthetic analog of coenzyme Q10 approved for treatment of LHON,is the only therapy specifically approved for the treatment of a hereditary optic neuropathic. Many other therapies, pursuing a range of treatment strategies, and underdevelopment. The progress of gene therapy in particular is exciting and may be approaching regulatory approval. For now, various forms of supportive care including low vision services, avoidance of mitochondria toxins, and genetic counseling remain crucial components of caring for patients with hereditary optic neuropathies.

Introduction Hereditary optic neuropathies (HONs) represent a heterogeneous group of genetically determined disorders characterized by dysfunction and degeneration of retinal ganglion cells (RGCs) and their axons (Yu-Wai-Man et al., 2011; Carelli et al., 2017). These disorders can occur either with isolated optic nerve degeneration or as part of a broader clinical syndrome (Carelli et al., 2017). Although individually uncommon, collectively these disorders constitute a significant cause of irreversible vision loss across the lifespan, from infancy to late adulthood (Newman, 2005; Newman & Biousse, 2004). Diagnosis of hereditary optic neuropathies has been aided by advances in genetic testing (Mackey et al., 2014). Currently, treatment options are limited but development of novel therapeutic options remains an area of active research (Osborne et al., 2018). This paper will first review the most common hereditary optic neuropathies, including their epidemiology, clinical features, and pathophysiology and then turn towards therapeutic options (Yu-Wai-Man et al., 2014).

Leber Hereditary Optic Neuropathy (LHON) First characterized by Thomas Leber in 1871, Leber Hereditary optic neuropathy (LHON) is the most common primary mitochondrial DNA (mtDNA) disorder (Leber, 1871; Wallace et al., 1988; Newman, 2005). It is often cited as the prototypical example of maternal, mitochondrial inheritance (Wallace et al., 1988; Newman, 2005). It is characterized by progressive vision loss that is most commonly sequential, with vision loss in the first eye followed by vision loss in the second eye months to years later (RiordanEva et al., 1995; Newman & Biousse, 2004). The vision loss of Leber hereditary optic neuropathy most commonly presents as progressive, painless central vision loss (Newman & Biousse, 2004; Sadun et al., 2000). This central vision loss may present as blurring and/or as central or cecocentral scotomas (Sadun et al., 2000). Dyschromotopsia is also frequently present, often early in the disease course (Newman & Biousse, 2004). Generally, one eye is affected first with second eye involvement following months to years later (Riordan-Eva et al., 1995). Second eye involvement occurs within 1 year in 97% of cases, although up to an 18-year interval in second eye involvement has been reported (Riordan-Eva et al., 1995). In a minority of cases, there is bilateral involvement at presentation (Newman, 2005). Initial visual impairment is frequently mild; some

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Zaidi, Moosa patients are even asymptomatic at presentation or only become aware of visual impairment in the first affected eye after covering the fellow, not yet affected, eye (Newman et al., 1991). However, symptoms usually progress to significant loss of visual acuity, usually worse than 20/200 (Newman et al., 1991; Carelli et al., 2004). The classic triad of signs associated with LHON is (1) circumpapillary telangiectatic microangiopathy, appearing as abnormal dilation and tortuosity of small capillaries surrounding the optic nerve head; (2) swelling of the peripapillary nerve fiber layer (pseudoedema), and (3) absence of corresponding disc or peripapillary leakage on fluorescein angiography (distinguishing the pseudoedema from the disc edema of inflammatory optic neuropathies) (Nikoskelainen et al., 1983; Sadun et al., 2000). However, disc appearance can also be normal initially (Newman, 2005). Late stages of the disease are associated with first temporal, and eventually diffuse, optic atrophy (Newman et al., 1991). Central or cecocentral scotomas can be detected on visual field testing (Sadun et al., 2000). Decreased color vision, reduced contrast sensitivity, and subnormal electroretinograms may also be detected (Holder et al., 2006). Corresponding to initially temporal disc atrophy and central visual field defects, the papillomacular bundle within the nerve fiber layers tends to be affected first (Barboni et al., 2010). At any given point in the disease course, an afferent pupillary defect may or may not be present based on the current symmetry of nerve involvement (Newman & Biousse, 2004). MRI brain and orbits is frequently obtained in patients with suspected LHON to exclude compressive or inflammatory causes of optic neuropathy (Rizzo et al., 2003). Most commonly MRI is normal in LHON but T2 hyperintensity of the nerves and contrast enhancement of the infraorbital nerve and optic chiasm can be seen (Rizzo et al., 2003). Therefore, presence of MRI abnormalities does not necessarily exclude LHON (Rizzo et al., 2003). Overall, the diagnosis of LHON is made based on clinical presentation supported by genetic testing and must be considered in any case of unexplained bilateral optic neuropathy (Wallace et al., 1988; Mackey et al., 2014). While most patients with LHON have ophthalmologic findings alone, 5–10% of patients will have additional systemic manifestations, which is then referred to as LHON plus disease (Carelli et al., 2017). These additional systemic manifestations are caused by the same primary LHON mtDNA mutations and represent a phenotypic extension of LHON rather than a separate genetic disorder (Carelli et al., 2017; Finsterer & Zarrouk-Mahjoub, 2016). Specifically, the same underlying mitochondrial dysfunction can also affect other tissues with high energy demands (Carelli et al., 2009). The most common extraophthalmologic organ systems affected are neurologic, including weakness, dystonia, tremor, parkinsonism, ataxia, peripheral neuropathy, and seizures; cardiac, particularly conduction abnormalities; and myopathy (Finsterer & Zarrouk-Mahjoub, 2016; Carelli et al., 2017). One important specific form of LHON plus disease is Harding disease, which refers to LHON co-existing with a multiple sclerosis (MS)like demyelinating disease (Harding et al., 1992; Palace, 2009). Harding disease is in fact more common than isolated LHON among women (Harding et al., 1992; Palace, 2009). The disease prevalence of symptomatic LHON is ~1–3 per 100,000 in most European populations, 3.2 per 100,000 in northeast England, ~1 per 30,000–50,000 in Japan, and ~1–2 per 100,000 in the US (Man et al., 2003; Yu-Wai-Man et al., 2011). In Australia, it causes ~2% of legal blindness in people younger than age 65 (Mackey et al., 1996). The mutation prevalence is 10–12 per 100,000 in population-based studies (Man et al., 2003). The typical age of onset is between 15 and 30 years of age, with peak age of onset in the second and third decades of life, although the reported age range of onset extends from 2 to 80 years (Newman, 2005). Interestingly there is some variation in average age of onset with mutation type, with the T14484C mutation associated with a significantly later onset than the G11778A mutation (Carelli et al., 2004). Male predominance is a notable feature of the disease, with males accounting for up to 80 to 90% of cases (Newman, 2005). The reason for this gender imbalance is unknown, although a susceptibility locus on the Y chromosome has been proposed (Hudson et al., 2007). The disease is characterized by incomplete penetrance with an estimated lifetime prevalence of 10–30% among mutation carriers overall, 30–50% among male carriers, and 5–15% among female carriers (Yu-Wai-Man et al., 2003; Hudson et al., 2007). With regards to environmental risk factors affecting penetrance, there is strong epidemiologic and mechanistic evidence for tobacco smoking and less strong evidence for alcohol (Kirkman et al., 2009). Notably, one study found 93% disease penetrance in male smokers compared to only 66% in non-smoking males and 33% in smoking females (Kirkman et al., 2009). Avoiding tobacco

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2026 Harvard Ophthalmology Residents’ Course smoking and limiting alcohol are therefore routinely recommended to known LHON carriers (Yu-Wai-Man et al., 2014). LHON is caused by mitochondrial mutations affecting NADH-ubiquinone oxidoreductase, also known as Complex I of the Electron Transport Chain (ETC) of oxidative phosphorylation (Wallace et al., 1988). This inner mitochondrial membrane protein complex catalyzes electron transfer from NADH to ubiquinone (CoQ10) (Hirst, 2013). This electron transfer is coupled to proton pumping across the inner mitochondrial membrane, which in turn establishes the proton gradient required for ATP synthesis by complex V (Hirst, 2013). Dysfunction of Complex I is thought to result in reduced ATP production and increased free-radical damage from production of reactive oxygen species (Carelli et al., 2009; Osborne et al., 2016). The unmyelinated papillomacular bundle is thought to be uniquely vulnerable to the resultant metabolic and oxidative stress, leading to retinal ganglion cell apoptosis and, eventually, atrophy and demyelination of optic nerves, chiasm, and tracts (Sadun et al., 2000; Osborne et al., 2016). Three primary mtDNA point mutations account for over 90% of cases of LHON: mutations G11778A, T14484C, and G3460A affecting mitochondrial genes ND1, ND4, and ND6 respectively (Brown et al., 1995). G11778A is the most common mutation, accounting for approximately 70% of cases in Northern Europe and 90% in Asian populations (Brown et al., 1995; Yu-Wai-Man et al., 2011). These mutations are usually homoplasmic, with heteroplasmy seen in 10–15% of patients (Chinnery et al., 2001). Consistent with mitochondrial genetics, inheritance is entirely maternal (Wallace et al., 1988). Although de novo mutations are rare, many patients with LHON do not have a known family history of LHON, likely due in part to incomplete penetrance (Hudson et al., 2007). At present, visual prognosis for LHON remains unfortunately poor, with most patients experiencing severe, permanent bilateral vision loss (Newman et al., 1991; Carelli et al., 2004). Most patients progress to legal blindness with final visual acuity of worse than 20/200 in both eyes, and frequently to counting fingers or hand motion vision, although progression to no light perception is rare (Newman et al., 1991; Newman, 2005). A typical time course of the disease is involvement of the first eye with progression to a nadir over weeks to a few months and involvement of the second eye weeks to month after the first eye and similarly reaching a nadir after two to three months (Riordan-Eva et al., 1995). After reaching a nadir, vision loss tends to stabilize in each eye such that most patients have stabilized by six months from vision loss onset and nearly all patients have stabilized by 12 months (Newman et al., 1991; Carelli et al., 2004). Further significant decline after stabilization is rare (Newman et al., 1991). A minority of patients (~10– 30%) may experience some degree of spontaneous partial visual recovery, usually years after onset, but full visual recovery remains rare (Carelli et al., 2004; Yu-Wai-Man et al., 2011). The culprit mutation strongly influences visual prognosis, with some level of spontaneous visual improvements in 35–60% of patients with the T14484C mutation, 15–25% of patients with the G3460A mutation, and only 4–15% of patients with the G11778A mutation (Carelli et al., 2004; Yu-Wai-Man et al., 2011). Earlier age of onset is associated with a higher chance of visual recovery, while tobacco and alcohol appear to worsen prognosis (Kirkman et al., 2009; Yu-Wai-Man et al., 2014).

Dominant Optic Atrophy (DOA) First described by the Danish ophthalmologist Poul Kjer in the late 19th century, Autosomal Dominant Optic Atrophy (DOA) also known as Kjer type optic atrophy, is the most common hereditary optic neuropathy (Kjer, 1959; Votruba et al., 1998). As its name indicates, DOA is characterized by autosomal dominant inheritance in contrast to the mitochondrial inheritance of LHON (Yu-Wai-Man et al., 2010). Among other features, it is also distinguished from LHON by earlier onset and a milder disease course (Yu-Wai-Man et al., 2010). DOA tends to present with gradual painless bilateral vision loss, often with symmetric involvement of both eyes (Votruba et al., 1998). The onset can frequently be insidious, with vision loss going unnoticed for years (Yu-Wai-Man et al., 2010). Initial presentation as reading difficulties in school age children is common (Votruba et al., 1998). Vision loss is slowly progressive and often stabilizes in adolescence or early adulthood; sudden or stepwise decline is not typical (Yu-Wai-Man et al., 2010). Visual acuity loss is usually mild to moderate with 70–80% maintaining visual acuity better than 20/200 (Yu-Wai-Man et al., 2010). However, marked inter- and intrafamilial variability in disease severity is observed and legal

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Zaidi, Moosa blindness can rarely occur (Votruba et al., 1998; Yu-Wai-Man et al., 2010). In addition to diminished central visual acuity, contrast sensitivity reduction and color vision loss, particularly decreased blue-yellow color discrimination, are also prominent features (Holder et al., 2006). Central or cecocentral scotomas can additionally be seen (Votruba et al., 1998). The classic fundoscopic finding of DOA is wedge-shaped temporal pallor, which can later progress to diffuse optic disc pallor (Kjer, 1959; Votruba et al., 1998). In addition to an atrophic optic nerve rim, a temporal gray crescent can be seen (Kjer, 1959). Correspondingly, optical coherence tomography (OCT) shows retinal nerve fiber layer (RFNL) thinning with temporal predominance (Barboni et al., 2013). Ganglion cell layer loss is also commonly seen on OCT (Barboni et al., 2013). Visual field testing shows central or cecocentral scotomas, while electrophysiology demonstrates reduced visual evoked potential (VEP) amplitudes and reduced N95 component on pattern ERG (pERG) (Holder et al., 2006). Tritanopia (blue-yellow dyschromatopsia) is a classic finding, although other studies find generalized dyschromatopsia to be most common (Votruba et al., 1998; Holder et al., 2006). Reflecting the usual symmetry of optic nerve involvement, a relative afferent pupillary defect tends to not be present (Newman & Biousse, 2004). MRI is typically normal (Yu-Wai-Man et al., 2010). Diagnosis is based on clinical findings, family history, and optic nerve appearance (Votruba et al., 1998; Yu-Wai-Man et al., 2010). Analogous to LHON and LHON plus disease, DOA can also present with extra-ophthalmic manifestations and is then termed DOA plus disease (Yu-Wai-Man et al., 2010). DOA plus disease occurs in approximately 10–20% of patients with OPA1 mutations (Yu-Wai-Man et al., 2010). The most common extra-ophthalmic manifestation is sensorineural hearing loss (Amati-Bonneau et al., 2008). Other frequently seen manifestations are progressive external ophthalmoplegia (PEO), ptosis, myopathy, ataxia, peripheral neuropathy, spasticity, and tremor (Amati-Bonneau et al., 2008; Yu-Wai-Man et al., 2010). Cardiomyopathy and cognitive involvement have also been rarely observed (Amati-Bonneau et al., 2008). The estimated prevalence of DOA ranges from approximately 1 in 12,000 to 1 in 50,000 (Yu-Wai-Man et al., 2010; Cohn et al., 2007). A higher prevalence of up to 1 in 10,000 is reported in Denmark, attributed to a founder effect (Kjer et al., 1996). Unlike LHON, males and females are equally affected in DOA (YuWai-Man et al., 2010). Overall, disease penetrance is approximately 70% (Cohn et al., 2007). In contrast to the strong evidence for tobacco smoking as an environmental trigger of LHON, no definite environmental triggers have been identified for DOA (Yu-Wai-Man et al., 2010). Nevertheless, avoidance of tobacco smoke, excess alcohol, and medications with known mitochondrial toxicity such as certain antibiotics and antivirals is usually recommended (Carelli et al., 2017). DOA is caused primarily (>75%) by mutations in the OPA1 gene (Alexander et al., 2000; Delettre et al., 2000). Located on chromosome 3q28–q29, OPA1 is a nuclear gene that encodes a mitochondrial inner membrane dynamin-related GTPase (Delettre et al., 2000). This protein is essential for mitochondrial fusion, mitochondrial cristae architecture maintenance, and stabilization of respiratory chain supercomplexes (Olichon et al., 2003; Cogliati et al., 2013). Mutations lead to fragmentation of the mitochondrial network and disruption of mitochondrial cristae, which in turn leads to decreased ATP production and increased oxidative stress from excess production of reactive oxygen species, which ultimately preferentially injures RGCs, especially in the papillomacular. which are selectively vulnerable (Olichon et al., 2003; Carelli et al., 2009). Thus the pathophysiology of DOA shares a pattern with that of LOA in terms of mitochondrial dysfunction ultimately damaging metabolically vulnerable RGCs, a pattern also seen in the pathophysiology of other hereditary optic neuropathies (Carelli et al., 2009; Yu-Wai-Man et al., 2011). There is significant heterogeneity in OPA1 mutations, with over 400 pathogenic variants identified, various mutation types (nonsense, frameshift, missense, etc.) and mutations distributed throughout the OPA1 gene including the GTPase domain, middle domain, and coiled-coil regions (YuWai-Man et al., 2010). As with LHON, de novo mutations are uncommon (Cohn et al., 2007). Most mutations exert an effect through haploinsufficiency (reduced functional OPA1 protein level) although some missense mutations exert dominant-negative effects (Amati-Bonneau et al., 2008). This dominantnegative effect is often associated with a DOA-plus phenotype (Amati-Bonneau et al., 2008; Yu-Wai-Man et al., 2010). Disease loci other than OPA1 have also been identified as leading to similar phenotypes but sometimes with different inheritance patterns including OPA3 (dominant; recessive mutations associated

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2026 Harvard Ophthalmology Residents’ Course with Costeff syndrome as below), OPA4 (dominant), OPA5 (dominant), OPA6 (recessive), OPA7/TMEM126A (recessive), and OPA8 (dominant) (Anikster et al., 2001; Yu-Wai-Man et al., 2011). The visual prognosis of DOA is generally favorable compared to LHON (Votruba et al., 1998; Yu-Wai-Man et al., 2010). Vision loss is usually slowly progressive and often stabilizes by early adulthood (Yu-WaiMan et al., 2010). Most patients retain functional vision throughout life, with more than 80% of patients maintaining visual acuity better than 20/200; severe visual impairment is uncommon (Votruba et al., 1998; Cohn et al., 2007). Some fluctuations in visual acuity may be observed but true spontaneous visual recovery, as sometimes seen in LHON, is rare (Yu-Wai-Man et al., 2010). OPA1 haploinsufficiency mutations are typically associated with isolated DOA and a better visual prognosis than dominantnegative OPA1 mutations which are associated with DOA-plus disease and with worse visual outcomes, with earlier onset and greater progression (Amati-Bonneau et al., 2008; Yu-Wai-Man et al., 2010).

Other Hereditary Optic Neuropathies While LHON and DOA are the two primary inherited disorders for which optic neuropathy occurs as an isolated or at least predominant (in the case of LHON plus and DOA plus disease) feature, optic neuropathy can also occur as part of numerous hereditary syndromes with multi-organ system manifestations (Yu-Wai-Man et al., 2011; Carelli et al., 2017). The most common of these syndromes is Wolfram syndrome, also known by the aptly descriptive acronym DIDMOAD (Diabetes Insipidus, Diabetes Mellitus, Optic atrophy, and Deafness) (Barrett et al., 1995). Wolfram syndrome is caused by mutations in WFS1 which encodes wolframin, an endoplasmic reticulum (ER) membrane protein that is involved in ER calcium homeostasis (Inoue et al., 1998). Loss of wolframin function leads to chronic ER stress and apoptosis of pancreatic β-cells, neurons, and retinal ganglion cells (Fonseca et al., 2005; Rigoli et al., 2018). Wolfram syndrome is therefore distinguished from LHON, DOA, and several other optic neuropathies by having the primary site of dysfunction be the endoplasmic reticulum rather than mitochondria (Rigoli et al., 2018). Reflecting the DIDMOAD name, core clinical features of the disease are diabetes mellitus, usually childhood-onset and insulin-dependent; progressive optic atrophy; diabetes insipidus; and sensorineural deafness (Barrett et al., 1995; Rigoli et al., 2018). Additional possible manifestations include ataxia, peripheral neuropathy, cognitive decline, depression, anxiety, neurogenic bladder, hydronephrosis, and hypogonadism (Rigoli et al., 2018). Prevalence of approximately 1 in 770,000 has been reported in the United Kingdom and approximately 1 in 710,000 in Japan (Barrett et al., 1995; Matsunaga et al., 2014). Prognosis is poor with typically severe (worse than 20/200) vision loss and death in the third to fourth decade, usually due to brainstem atrophy and consequent central respiratory failure (Barrett et al., 1995; Rigoli et al., 2018). Costeff Syndrome, also known as 3-methylglutaconic aciduria type III, is a syndrome characterized by optic atrophy with extrapyramidal neurologic disease (Costeff et al., 1989). Autosomal recessive, and caused by biallelic mutations in OPA3, it is distinct from dominant OPA3-associated optic atrophy (Anikster et al., 2001). OPA3 encodes an inner mitochondrial membrane whose dysfunction leads to impaired mitochondrial metabolism, abnormal mitochondrial morphology, and disrupted lipid and organic acid metabolism, including elevated 3-methylglutaconic acid (Anikster et al., 2001; Wortmann et al., 2013). Core clinical features include childhood-onset, bilateral, progressive, optic atrophy; later-onset extrapyramidal movement disorder with dystonia, spasticity, and Parkinsonion features; and cognitive impairment of variable severity (Costeff et al., 1989; Anikster et al., 2001). Basal ganglia involvement can be seen on neuroimaging in some cases (Anikster et al., 2001). Elevated urinary 3-methylglutaconic acid gives the disease one of its names and aids in diagnosis, which is ultimately confirmed through OPA3 genetic testing (Anikster et al., 2001; Wortmann et al., 2013). Leigh syndrome, also known as Subacute Necrotizing Encephalomyelopathy, was first described in 1951 by British neuropsychiatrist, Archibald Denis Leigh (Leigh, 1951). It is a severe early-onset mitochondrial encephalopathy caused by defects in oxidative phosphorylation and characterized by symmetric basal ganglia and brainstem lesions and progressive neurologic decline (Rahman et al., 2017). It is genetically heterogenous and can be caused by nuclear or mitochondrial DNA mutations and can display autosomal recessive (most common), X-linked, and maternal inheritance (Rahman et al., 2017). Mutations most commonly affect respiratory chain Complex I (same as LHON), but Complexes II, IV, and V can also be

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Zaidi, Moosa affected (Rahman et al., 2017). Resulting defective oxidative phosphorylation results in decreased ATP production, lactate elevation, and neuronal energy failure, with preferential damage to selectively vulnerable basal ganglia, brainstem nuclei, and cerebellum (Rahman et al., 2017). Onset is usually in infancy or early childhood (Leigh, 1951; Rahman et al., 2017). Progressive neurologic dysfunction including brain stem dysfunction is seen, manifesting as developmental regression, hypotonia, ataxia, dystonia, seizures, abnormal eye movement (including ophthalmoplegia and nystagmus), dysphagia, central respiratory failure, and failure to thrive (Rahman et al., 2017). Median age of death is 2–3 years (Rahman et al., 2017). Optic atrophy is seen in a minority of Leigh syndrome patients (~15–20% of cases), typically alongside other neurologic and ophthalmologic manifestations (Rahman et al., 2017). Hereditary polyneuropathies and ataxia can include optic disc atrophy among their manifestations (Carelli et al., 2017). Charcot Marie Tooth (CMT) disease is a hereditary peripheral polyneuropathy that causes distal muscle weakness and atrophy, length-dependent sensory loss, foot deformities (pes cavus, hammer toes), and gait abnormalities (Skre, 1974). Optic atrophy can uncommonly be present, particularly with the CMT2A subtype and rarely with the CMT1A subtype (Züchner et al., 2004; Pareyson et al., 2017). Spinocerebellar ataxias (SCAs) are a heterogeneous group of inherited neurodegenerative disorders whose core feature is progressive cerebellar ataxia; optic atrophy occurs in some subtypes, most notably SCA7, in which visual loss may precede ataxia (David et al., 1997). Friedreich’s ataxia is an autosomal recessive neurodegenerative disorder caused by mutations in the frataxin gene, specifically GAA trinucleotide repeat expansions in intron 1, which causes mitochondrial dysfunction secondary to mitochondrial iron accumulation (Campuzano et al., 1996). Disease features include progressive cerebellar ataxia, dysarthria, pyramidal signs, skeletal deformities, cardiomyopathies, and optic atrophy in 10–30% of cases, which is often mild and slowly progressive (Harding, 1981; Fortuna et al., 2009). Optic atrophy can also be seen as a feature of numerous systemic metabolic disorders (Yu-Wai-Man et al., 2011). Mitochondrial Encephalomyopathy, Lactic Acidosis, and Stroke-Like Episodes (MELAS) is as multisystem mitochondrial DNA disorder characterized by stroke-like episodes, encephalopathy, and lactic acidosis due to defective mitochondrial protein synthesis and impaired oxidative phosphorylation (Hirano et al., 1992). Significant phenotypic variability is present, attributable to heteroplasmy (Chinnery et al., 1997). Ophthalmic manifestations, when present, include optic atrophy and pigmentary retinopathy (Hirano et al., 1992). Myopathy, short stature, sensorineural hearing loss, and diabetes mellitus are additionally seen (Hirano et al., 1992). NARP (neuropathy, ataxia, retinitis pigmentosa) is a mitochondrial DNA disorder, most commonly due to mutations in MT-ATP6, which encodes a subunit of ATP synthase (Complex V), and can cause optic atrophy in some patients, although the primary ophthalmologic manifestation is “salt-and-pepper” pigmentary retinopathy which progresses to retinitis pigmentosa (Holt et al., 1990). Non-ophthalmologic features are sensory greater than motor peripheral neuropathy, cerebellar ataxia, seizures, and learning difficulties (Holt et al., 1990). Additional hereditary syndromes that can include optic atrophy as part of a wide constellation of features are lysosomal and leukodystrophy-related disorders, including metachromatic leukodystrophy, Krabbe disease, neuronal ceroid lipofuscinoses, and Nieman-Pick disease; and peroxismal disorders, particularly Zellweger Spectrum Disorders and X-Linked Adrenoleukodystrophy (van der Knaap & Valk, 2005; Kemp et al., 2012).

Treatment Options for Hereditary Optic Neuropathies With currently limited options for definitive therapy for hereditary optic neuropathies, supportive care organized across multiple aspects remains a cornerstone of providing optimal care to patients with hereditary optic neuropathies and their families (Yu-Wai-Man et al., 2014; Carelli et al., 2017). Considering the progressive nature of many of these diseases, early low vision referral is pursued, frequently at diagnosis (Binns et al., 2012). This early referral allows patients to start to build familiarity with optical aids, such as electronic magnifiers; contrast enhancement strategies, such as reverse polarity screws; and familiarity with orientation and mobility training before their dependence on these measures increases (Binns et al., 2012). Relatedly, patients should be connected to educational and occupational counseling, which can help patients navigate accommodations for visual disability (American Academy of Ophthalmology, 2020). Patients additionally benefit from screening for depression and anxiety with referral to mental services as needed (Cimarolli et al., 2015). Genetic counseling should be offered to

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2026 Harvard Ophthalmology Residents’ Course patients and their family members including discussion of the inheritance pattern of their specific disease, and the pattern of penetrance and expressivity that modulates the inheritance pattern (Newman & Biousse, 2004; Yu-Wai-Man et al., 2014). This includes preconception genetic counseling on the risk of transmitting disease to offspring and discussion of reproductive options that may mitigate this risk (Biesecker & Peters, 2001). Male patients with hereditary optic neuropathies under mitochondrial inheritance can be reassured of no possibility of transmitting disease to offspring (Wallace et al., 1988). A challenge specific to genetic counseling for mitochondrial DNA disorders is that heteroplasmy limits the reliability of prenatal testing and the reliability of pre-implantation genetic testing (Chinnery et al., 2000). In vitro fertilization with mitochondrial donation is a recently developed inheritance risk reduction strategy for mtDNA disorders, but is unavailable in most countries (Craven et al., 2010; Gorman et al., 2018). Avoidance of mitochondrial toxins including tobacco smoke, excess alcohol and certain medications such as ethambutol and linezolid is routinely recommended for all patients with hereditary optic neuropathies; this recommendation is strongest for avoidance of tobacco smoke in patient with LHON (Kirkman et al., 2009; Yu-Wai-Man et al., 2014). Finally, many patients also find it helpful to be connected to patient support groups for their disease (Carelli et al., 2017). Optimization of systemic health is recommended to patients with hereditary optic neuropathies (Carelli et al., 2017; Yu-Wai-Man et al., 2014). Beyond general recommendations for good health, specific considerations include ensuring tight glycemic control in patients with diabetes, given that diabetic ischemia may exacerbate hereditary optic nerve vulnerability (Newman & Biousse, 2004) and screening for and treating any nutritional deficiencies, with special attention to B12, folate, thiamine, and copper (Sadun et al., 2012; Pfeffer et al., 2012). Monitoring and management of possible thyroid disease is also given special attention given that dysthyroid optic neuropathy can exist alongside and exacerbate HONs (Bartalena et al., 2016). Finally, the possible extra-ophthalmologic manifestations of many HONs must be considered (Carelli et al., 2017). A multidisciplinary approach, with collaboration between multiple specialties, is frequently required to provide optimal care (Carelli et al., 2017). Special considerations include mandatory screening for cardiac conduction abnormalities in patients with LHON (Finsterer & Zarrouk-Mahjoub, 2016), audiologic screening in patients with DOA (Amati-Bonneau et al., 2008), and endocrine surveillance in patients with Wolfram syndrome (Rigoli et al., 2018). With regards to pharmacologic therapies, to date only one medication has achieved regulatory approval for the treatment of a hereditary optic neuropathy (European Medicines Agency, 2015). Idebenone is a synthetic analog of Coenzyme Q10 (CoQ10), with a shorter and less lipophilic tail that facilitates penetration through mitochondrial membranes (Giorgio et al., 2012). It is able to directly shuttle electrons from NADH to Complex III in the mitochondrial electron chain, bypassing Complex I, which is dysfunctional in LHON (Giorgio et al., 2012). It is currently approved for use in LHON in a limited number of countries including those in the European Union, UK, and South Korea on the basis of the RHODOS and LEROS trials (Klopstock et al., 2011; Catarino et al., 2020). Both studies indicated early initiation of idebenone gives the most benefit (Klopstock et al., 2011; Catarino et al., 2020). Idebenone has not yet been approved in the U.S., where it remains under FDA review, but is expected to be approved by early 2026 (Yu-Wai-Man et al., 2024). It is not approved for use in any hereditary optic neuropathy other than LHON (European Medicines Agency, 2015). It has been investigated for use in Friedrich’s ataxia, Alzheimer disease, and Duchenne Muscular Dystrophy but has failed to obtain approval for any of these other conditions (Buyse et al., 2011; McGarry et al., 2016). Several vitamins, cofactors, and antioxidants are often recommended as adjunctive pharmacological therapy, with the goal of improving mitochondrial function and reducing oxidative stress (Pfeffer et al., 2012; Sadun et al., 2012). Specific compounds include Coenzyme Q10, iron, copper, Thiamine (B1), Riboflavin (B2), Niacin (B3), Vitamin B12, Folate, vitamin CE, and Vitamin E (Pfeffer et al., 2012). Often many of these compounds are supplemented in combination as part of a mitochondrial “cocktail” (Pfeffer et al., 2012). Given low perceived risk of side effects and plausible benefit, the supplements are frequently recommended by individual practitioners (Sadun et al., 2012). However, even as there is some evidence of improvement of intermediate metabolic markers and plausibility of benefit, there has been no evidence of clinical benefit (Pfeffer et al., 2012).

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Zaidi, Moosa Among the pharmacologic therapies still under development, perhaps most exciting is gene therapy (YuWai-Man et al., 2011). Gene therapy promises to most directly correct the underlying defect of hereditary optic neuropathies (Guy et al., 2017). The eye is a ready target for gene therapy given that local administration of viral vectors can be achieved through intravitreal injection, reflected in the status of Luxturna, a gene therapy for retinitis pigmentosa, as the first gene therapy overall approved for in vivo use in humans (Russell et al., 2017). The primary target of current development gene therapy efforts for HON is LHON caused by MT-ND4 mutations (Guy et al., 2017; Yu-Wai-Man et al., 2020). Given the challenges of transporting genetic material across mitochondrial membranes, most recent trials focus on allotopic expression of mitochondrial (Guy et al., 2017). With this approach, the desired gene product is recoded using the nuclear genetic code, addended with a mitochondrial targeting sequence (MTS) at the N-terminal end, and inserted into the nuclear DNA, with the goal that the gene product, after being produced in the cytoplasm, is transported to the mitochondria (Guy et al., 2017). Thus far, only one gene therapy for hereditary optic neuropathy has completed phase 3 trials (Yu-WaiMan et al., 2020). Lenadogene nolparvovec is an intravitreal adeno-associated virus-2 (AAV2) vectorbased gene therapy that targets LHON (MT-ND4 mutation) (Yu-Wai-Man et al., 2020). It initially completed the phase 3 RESCUE and REVERSE trials (Yu-Wai-Man et al., 2020; Klopstock et al., 2019). In both these trials, there was on average improvement in the treated eye exceeding what would be expected by natural history, which is promising (Yu-Wai-Man et al., 2020; Klopstock et al., 2019). However, in both trials there was a similar level of improvement in the fellow, untreated eyes which were intended to serve as controls; and the primary endpoint, visual acuity improvement relative to control, was not reached in either trial (Yu-Wai-Man et al., 2020; Klopstock et al., 2019). It has been hypothesized that improvements in the fellow eyes could have been from transfer of gene therapy genetic material from the injected eye to the eye (Yu-Wai-Man et al., 2020; Feuer et al., 2020). The REFLEX trial attempted to account for this potential confounding effect by comparing simultaneous bilateral treatment to delayed bilateral injection (Newman et al., 2021). Promisingly, there was significant improvement in many patients, sustained over long-term (~5 year) follow up and with no major systemic safety signals (Newman et al., 2021). However, because of similar results between the simultaneous versus delayed bilateral treatment arms, and no true sham-treated parallel control group, the trial was again unable to definitively establish treatment efficacy to the standard required for regulatory approval (Newman et al., 2021). NR082 / esonadogene imvoparvovec is a second AAV2-based gene therapy targeting LHON with MTND4 mutation (Guy et al., 2017). Except for some further optimization of the cassette technology, esonadogene imvoparvovec is a very similar technology to lenadogence nolparvove (Guy et al., 2017); however, its Phase III trial currently underway addresses the limitations of the lenadogence nolparvove trials by having a parallel control sham-treatment group. Trial results have not yet been reported. Gene therapy for DOA remains in preclinical stages; potential challenges to clinical development relative to LHON include the larger size of the OPA1 gene (near the packaging limit of AAV vectors), much greater heterogeneity in mutations, and slower progression of DOA, which is expected to make establishing clinical efficacy more challenging (Yu-Wai-Man et al., 2010). Closely related to gene therapy, RNA-targeted therapies are being developed for nuclear-gene hereditary optic neuropathies, most prominently DOA (Yu-Wai-Man et al., 2010; Carelli et al., 2017). The primary technology being explored is antisense oligonucleotides (ASOs), which are short, synthetic singlestranded nucleic acids designed to modulate gene expression by binding specific nucleotides (Bennett & Swayze, 2010). Possible mechanisms by which ASOs can have their effect include altering splicing, stabilizing transcripts, block degradations and modulating translation (Bennett & Swayze, 2010). ASOs are of particular interest for OPA1 mutation DOAs given that the OPA1 gene presents a challenge to gene therapy as above and given that most pathogenic OPA1 mutations cause reduced functional protein via haplosufficiency, so that boosting expression of the healthy allele via ASOs is theorized to be ameliorative (Amati-Bonneau et al., 2008; Yu-Wai-Man et al., 2010). Preclinical data from patient derived fibroblasts and non-ocular animal models have been promising (Bonnet et al., 2008).

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2026 Harvard Ophthalmology Residents’ Course Several other therapies under investigation attempt to treat HONs more indirectly by optimizing mitochondrial metabolic functioning (Pfeffer et al., 2012). Nicotinamide (vitamin B3), nicotinamide riboside (NR), and nicotinamide mononucleotide (NMN) are NAD+ precursors that are theorized to increase NAD+ levels, which could improve the mitochondrial function (Cantó et al., 2015). PGC-1α pathway activators aim to increase mitochondrial biogenesis and oxidative capacity (Scarpulla, 2011). These approaches are supported by preclinical data with markers such as improved RGC survival in experimental data, but currently lack clinical evidence (Osborne et al., 2016). EPI-743 (vatiquinone) is a synthetic parabenzoquinone redox-modulation agent that promotes regeneration of reduced glutathione and supports mitochondrial redox homeostasis (Sadun et al., 2012). Primarily investigated for Friedrich’s ataxia, it has been hypothesized to be potentially helpful to multiple hereditary optic neuropathies (Zesiewicz et al., 2018). Several other quinolone therapies are also being explored as possible therapies for mitochondrial disorders (Pfeffer et al., 2012). Elamipretide (SS-31) is a mitochondria-targeting peptide that binds cardiolipin in the inner mitochondrial membrane and is thought to have stabilized cristate structures and improved electron transport efficiency (Szeto, 2014). It has been evaluated in early-phase LHON studies using topical administration, which showed safety but not efficacy (although topical administration likely limited penetration to neuroretinal tissue) (Klopstock et al., 2019). Finally, modulation of apoptotic pathways has also been studied, although clinical data again remains limited (Carelli et al., 2017).

Conclusion Hereditary optic neuropathies are a heterogenous group of disorders characterized by degeneration of retinal ganglion cells. LHON and DOA are distinguished as the two inherited disorders in which optic nerve degeneration is the sole or predominant degeneration, but the full array of inherited disorders that include optic nerve degeneration as at least one of its features is far broader. For example, many neurodegenerative disorders can include optic nerve degeneration alongside degeneration of other tissues. While heterogenous overall, this full array of disorders shares certain themes, such as pathophysiology involving the selective vulnerability of RGCs to metabolic and oxidative disorders and symptoms involving progressive dyschromatopsia, loss of visual acuity, and scotomas, as might be expected of optic nerve disorders. Optimizing supportive measures including smoking cessation, genetic counseling, referral to low vision specialist, and facilitating psychosocial support, remains crucial to caring for patients with hereditary optic neuropathies and their families. Currently, only one medication has received regulatory approval for the treatment of hereditary optic neuropathy, ibedenone for the treatment of LHON. Nevertheless, numerous additional pharmacologic approaches to hereditary optic neuropathies are being investigated. Among these, gene therapy in particular has demonstrated exciting clinical results and the compelling possibility of definitively modifying these genetic diseases at their pathophysiologic origin.

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