Dry age-related macular degeneration

Multiple questions and issues pertaining to the use of the epiretinal prosthesis for restoring vision lost from dry AMD.

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Initial outcomes from a single-centre feasibility study investigating the safety and utility of the Argus II Retinal Prosthesis (Second Sight Medical Products) in patients with dry age-related macular degeneration (AMD) justify expanding the research into a larger, multi-site trial, accoring to Paulo Stanga MD. The experience, however, also underscores the need to resolve multiple questions and issues pertaining to the use of the epiretinal prosthesis for restoring vision lost from dry AMD. Dr Stanga is Professor of Ophthalmology, University of Manchester, UK, and principal investigator for the three-year study that included five patients operated on at Manchester Royal Eye Hospital. Summarising findings from available follow-up, which ranged from six to 15 months, he said: “Testing in all patients showed visual function in the area of the geographic atrophy (GA) that was confirmed absent preoperatively. In addition, patients reported finding it easier to see facial characteristics. Importantly, no patients reported confusion when operating the retinal prosthesis with their remaining peripheral vision and both eyes open. We can also say that the patients retained their native peripheral vision, even if they suffered adverse events, and that they could integrate their native peripheral vision with their artificial central vision.” The adverse events included development of proliferative vitreoretinopathy (PVR) in two patients who responded successfully to pars plana vitrectomy with silicone oil insertion. In addition, hypotony occurred at 6 months after surgery in one patient who also had a good outcome after intraocular injection of silicone oil. UNIQUE CONCERNS Dr Stanga noted that whether PVR would occur was one of the three greatest worries surrounding implantation of the retinal prosthesis in the dry AMD patients. The other two related to the development of visual confusion or diplopia and potential for conversion to wet AMD. “We are working on identifying strategies to reduce the risk of PVR, but the experience so far also raises the question of whether it would be feasible to use a subretinal prosthesis in patients with dry AMD,” Dr Stanga said. Ongoing research is also focusing on determining the resolution of the artificial vision achieved by the AMD patients as well as optimisation of the prosthesis and of the postoperative rehabilitation for this population. “The device we are using now was designed for patients with retinitis pigmentosa (RP), and we know that rehabilitation will be different for AMD patients who unlike RP patients have maintained their peripheral vision,” Dr Stanga said. The Argus II has the CE mark and FDA approval for use in patients with RP, of which about 200 have been implanted so far. Dr Stanga noted that patients with advanced dry AMD are expected to have a greater chance for regaining central vision relative to those with RP because the bipolar cells, ganglion cells, optic nerve head, and cortex are preserved in eyes with GA. “The fact that the AMD patients also maintain their peripheral vision, however, raised questions about effects on the preserved peripheral vision and whether the native peripheral vision could be integrated with the newly acquired central vision,” Dr Stanga said. STUDY DETAILS The five patients enrolled in the pilot study ranged in age from 69 to 81 years. Eligibility criteria required them to have ETDRS logMAR visual acuity of 1.0 or worse in both eyes, subfoveal GA confirmed by fundus autofluorescence, and scotoma within the central 20° confirmed by microperimetry. The retinal prosthesis was implanted in the worse eye. “The array was tacked monomanually or bimanually, but I prefer the bimanual technique for these patients because of the need to place the array within the area of GA and so that it does not interfere with the peripheral vision,” Dr Stanga said. He added that swept-source optical coherence tomography, which has good penetration through the implant, is very beneficial for assessing the distance between the array and the retina. Autofluorescence imaging showed the arrays were well localised to the area of GA. Paulo Stanga: p.stanga@retinaspecialist.co.uk