Preoperative treatment

Optimising outcomes for diabetic patients

Preoperative treatment of retinal pathology essential to good outcome of cataract surgery in diabetic patients. Roibeard O’hEineachain reports

In cataract patients with diabetic retinopathy, detailed informed consent and additional planning of the perioperative period can optimise surgical outcomes and help manage expectations, reports Catarina Pedrosa MD, Lisbon, Portugal.

“Cataract surgery may improve vision in patients with retinal diseases, but it is crucial to monitor and treat the underlying retinal pathology,” Dr Pedrosa told the 25th ESCRS Winter Meeting.

She noted that the presence of diabetic retinopathy can influence every aspect of cataract surgery, from the timing of surgery, to the surgical technique, the type of IOL used and the final outcome. She added that the prevalence of cataract among young diabetic patients is higher than that among others in their age-group. The cataracts occurring in eyes of diabetic patients usually involve cortical and posterior subcapsular opacities.

RETINAL DISEASE Dr Pedrosa also pointed out that cataract surgery may exacerbate retinal disease in patients with diabetic retinopathy. In such eyes the procedure can break down the blood-retinal barrier and the bloodaqueous barrier enhancing intraocular inflammatory response. That, in turn, raises risk of retinopathy progression. Diabetic retinopathy also increases the risk of intra- and postoperative complications. Moreover, eyes of diabetic patients often have delayed wound healing and higher risk of developing epithelial defects or recurrent erosions due to the impairment of epithelial basement membranes and epithelial-stromal interactions. They are also more prone to dry eye because of diabetic neuropathy.

Small pupil is common in diabetic patients and frequently occurs in eyes that have undergone laser photocoagulation making cataract surgery technically challenging. Alterations in pupillary function are mainly due to autonomic neuropathy, which mainly affects the sympathetic innervation of the iris dilator. Commonly used mydriatics and anticholinergic agents are less effective in eyes with the condition and the addition of directly acting sympathomimetics may be required, Dr Pedrosa said.

Although there is no direct evidence that diabetes influences the final outcome of biometry, there are special considerations regarding the eyes with diabetic macular oedema and those filled with silicone oil, Dr Pedrosa said. Axial length measurements in eyes with cystoid macular oedema (CME) obtained using applanation ultrasound differ significantly both statistically and clinically from those obtained with the IOLMaster. In addition to the indentation effect, the ultrasound devices measure the axial length from the corneal apex to the vitreoretinal interface, whereas the IOLMaster measures the axial length from the apex of the cornea to the retinal pigmented epithelium, being less affected by retinal thickening.

In eyes treated with silicone oil, the remnants of the vitreous base and the partial filling with silicone oil creates optical distortions that can make optical biometry findings inaccurate, with only a third of eyes within 1.0D of their refractive target postoperatively. Dr Pedrosa said that best practice is to perform biometry before injecting silicone oil. If that is not possible, measurement of the second eye or biometry after silicone oil removal are probably the best alternatives. She also recommended the use of convex-plano monofocal polymethyl methacrylate or foldable hydrophobic acrylic intraocular lenses (IOLs) with large optic diameter in these patients.

In general, when choosing an IOL for patients with macular lesions or who are at a high risk for progression, hydrophobic acrylic monofocal IOLs are the most appropriate, and multifocal lenses are best avoided, as are hydrophilic IOLs because they can be more prone to opacities, she added.

Phacoemulsification in vitrectomised eyes is surgically more challenging because of the relative ocular hypotony and the possible presence of anterior synechiae associated with small pupils, Dr Pedrosa said. Furthermore, in such eyes the anterior chamber is deeper and fluctuating, the zonules are also weaker and the posterior capsule may be fibrotic or calcified because of surgical trauma.

She noted that the reduced vitreous pressure in vitrectomised eyes makes the capsulorhexis easier to perform and makes the running of the rhexis less likely to occur. Hydrodissection and hydrodelineation should be performed carefully and thoroughly. In eyes where the lens is adherent to the capsule, viscodissection may be necessary and, after irrigation aspiration, a cannula can be used to carefully release and aspirate the remaining cortical material, avoiding capsular rupture. Using low flow parameters will reduce the stress on the zonules by reducing the fluctuation of the anterior chamber. Complete aspiration of the cortical material will reduce the risk of postoperative inflammation.

MACULAR OEDEMA Patients with diabetes are at higher risk of diabetic macular oedema (DME) and CME after cataract surgery, with an incidence of 4%. The risk rises with the staging of the ocular pathology and the systemic pathology and also the hardness of the cataract. The ESCRS PREMED study showed that subconjunctival triamcinolone acetonide (40mg) reduced the risk of postoperative CME in diabetics who underwent phacoemulsification, when applied additionally to the standard regimen of perioperative topical bromfenac and dexamethasone phosphate.

“Visual acuity improves after cataract surgery in patients with diabetic retinopathy regardless of the degree of disease, although eyes with the condition may take longer to heal and achieve a stable postoperative refraction. It is important to treat the disease preoperatively and to maintain vigilance in diabetic patients after cataract extraction with serial dilated funduscopic examinations, even when central macular oedema is not present immediately prior to cataract surgery. Eyes with prior DME treatment or non-central involved DME have a particularly high risk of developing central-involved ME after cataract surgery,” Dr Pedrosa added.