What’s Next for RP?

by Tan Sher Lynn

To date, there’s no cure for retinitis pigmentosa (RP), an inherited disease that can lead to blindness. However, recent studies on retinal lasers and RP showed promising results in slowing disease progression and improving function.

Retinitis pigmentosa is a debilitating inherited eye disease for which effective treatment is not yet known, despite advances in drugs, genetics, and immunotherapy. 1 In fact, it is the fourth leading cause of blindness in the world. 2

Nevertheless, all hope is not lost. It was discovered that the use of retinal lasers may help preserve sight in patients with photoreceptor degeneration, as demonstrated by studies on animals and humans.

A review on laser treatment for RP found six studies involving animal models and three studies involving human subjects in the PubMed database.3

Among them, a 2019 study4 published in the Translational Vision Science & Technology journal found that retinal laser therapy preserved photoreceptors in rats with Mer tyrosine kinase receptor (MERTK)related RP.

In the study, the authors used three modalities, including photocoagulation with various pattern densities, selective RPE therapy (SRT), and non-damaging retinal therapy (NRT).

Laser treatments were performed on the right eyes of the Royal College of Surgeons (RCS) rats, while the left eyes were used as control. Rats were monitored for six months after treatment using electroretinography, optical coherence tomography, and histology.

The authors found that photocoagulation led to the preservation of photoreceptors on a long-term basis, with the degree of the benefit dependent on the laser pattern density. Pattern photocoagulation of about 15% of the photoreceptors (eyes treated with a 1.5 spot size spacing) demonstrated the best morphologic and functional preservation during the six-month follow-up. Meanwhile, SRT-treated eyes demonstrated short-term morphologic preservation, but no functional benefit. Finally, NRTtreated eyes did not show any observable preservation benefit from the treatment.

Meanwhile, a 2018 study5 published in the peer-reviewed journal Eye examined the effect of subthreshold diode micropulse laser (SDM) on pattern electroretinography (PERG) and visual function in RP. Twenty-six eyes of 15 patients were included, of which seven were male and eight were female, aged between 16 and 69 years.

Each eye was evaluated by PERG one week prior, and one month after, SDM treatment, which showed that retinal function improved by all indices. Meanwhile, omnifield resolution perimetry (ORP) testing was performed on 23/26 eyes, which showed that 17 (81%) eyes were improved by all measures compared to control eyes after SDM treatment.

The study concluded that SDM improved mesopic visual fields and mesopic and photopic visual acuity in RP regardless of the underlying genomics. As such, SDM may slow progression and reduce visual loss related to RP. It also suggested that new RP treatments be evaluated by confirmation of improved retinal electrophysiology function.

Although there’s a promising role for retinal lasers in the treatment of RP, currently, there isn’t enough data to support laser treatment as a standard procedure to treat RP in humans.

Retinal lasers should be investigated more extensively in clinical trials, with the hope that one day this modality could be widely used to benefit millions of people affected by RP worldwide.

1. Sacchetti M, Mantelli F, Merlo D, Lambiase A. Systematic review of randomized clinical trials on safety and efficacy of pharmacological and nonpharmacological treatments for retinitis pigmentosa. J Ophthalmol. 2015;2015:737053.

2. Bourne RR, Stevens GA, White RA. et al. Vision Loss Expert Group Causes of vision loss worldwide, 1990-2010: a systematic analysis. Lancet Glob Health. 2013;1:339349.

3. Gawęcki M. Laser treatment in retinitis pigmentosa — a review. Lasers Med Sci. 2020;35(8):1663-1670.

4. Kang S, Lorach H, Bhuckory MB, Quan Y, Dalal R, Palanker D. Retinal Laser Therapy Preserves Photoreceptors in a Rodent Model of MERTK-Related Retinitis Pigmentosa. Transl Vis Sci Technol. 2019;8(4):19.

5. Luttrull JK. Improved retinal and visual function following panmacular subthreshold diode micropulse laser for retinitis pigmentosa. Eye (Lond). 2018;32(6):1099-1110.