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Learning from retinal implants

Experience with discontinued implant provides important insights.

Cheryl Guttman Krader

Posted: Sunday, September 1, 2019

Taking into account reimbursement obstacles and outcomes that fall short of today’s patients’ expectations, Retina Implant AG shareholders recently resolved to dissolve the company. Therefore, production of Retina Implant Alpha AMS, the company’s subretinal visual implant, has been discontinued.
Looking back, however, valuable information can be gleaned from experience with the electronic subretinal prosthesis RETINA IMPLANT Alpha AMS and its earlier generation version (RETINA IMPLANT Alpha IMS), said Katarina Stingl MD, at the Annual Meeting of the Association for Research in Vision and Ophthalmology in Vancouver, Canada.
Dr Stingl, University of Tübingen, Tübingen, Germany, has 12 years of clinical experience with the subretinal visual implants involving patients implanted in clinical trials and post-commercialisation. Highlighting four issues, she said that the experience provided proof of concept that the subretinal implant approach could restore vision to patients with complete blindness from photoreceptor degeneration. The approach, however, had limitations.
VISUAL ACUITY
“Visual acuity (decimal) will never be better than 0.1, the visual field is only a square of 10º to 15º, and there is no colour vision and no automatic adaptation to light levels,” said Dr Stingl.
As another caveat, which was Dr Stingl’s second point, it was seen that outcomes vary individually. Approximately one-half of patients could recognise shapes and rough details. Of the rest, about one-half were able to localise objects, but the remaining patients perceived no useful visual information from the implant in their daily life.
“Although all patients who received the implant were selected based on the same inclusion and exclusion criteria, not everyone benefited in the same way. The individual differences in outcomes were sometimes explainable, but sometimes were a black box for us,” she explained.
FOVEAL ECCENTRICITY
Not surprisingly, implant location was one factor that made a difference. Dr Stingl’s third point was that foveal eccentricity matters. Higher visual functions – location perception, grating acuity, motion perception, and ability to read letters – were almost only possible in patients whose implant was in a subfoveal versus a parafoveal location, she said.
Lastly, Dr Stingl noted that the subretinal implant approach had a good safety profile. Surgery-related adverse events included cases of haemorrhage and IOP increase, but they resolved within days to a few weeks after implantation.
Over 12 years of clinical experience, the implant showed good long-term biocompatibility and there were no cases of endophthalmitis or inflammation. Retinal thickness measured by OCT for six months after surgery remained unchanged.

Katarina Stingl: Katarina.Stingl@med.uni-tuebingen.de