Abstract
Purpose: :
In a prior pilot study, a microphotodiode-based artificial silicon retina chip (ASR) was implanted into the subretinal space of 6 retinitis pigmentosa (RP) patients and followed for 18 months. The ASR electrically stimulated the retina, producing phosphenes in retinotopically appropriate locations in some patients but also induced retinal neurotrophic rescue effects in all patients that consisted of improved visual acuity, contrast and color perception and enlarged visual fields. At the end of the study, the 6 patients along with 4 additional implant patients were followed by the author for ~8 years in his clinical practice and long-term ASR function was documented along with the patients’ neurotrophic responses.
Methods: :
6 of the 10 patients had vision in the range that allowed for more standardized vision testing and were followed with ETDRS charts and a 4-alternative forced choice paradigm Grating Acuity Test (GAT) that utilized random computerized presentations of square wave gratings across spatial frequencies. 5 years after implantation, a patient expired from an unrelated event, and histological examination of the eyes was performed and the implant was tested for function.
Results: :
Over ~8 years, the ASR was well tolerated and improvement and/or slowing of vision loss of the implanted eyes versus un-implanted eyes occurred in all 6 patients. At their last examination, the implanted eyes of all 6 patients exhibited improved ETDRS and/or GAT acuity compared to before implantation whereas deterioration occurred in all of the opposite unimplanted eyes. The explanted ASR showed minimal physical disruption and demonstrated excellent electrical activity suggesting a functional life of ~20 years.
Conclusions: :
ASR chip implanted RP patients demonstrated prolonged neurotrophic rescue of visual acuity that was consistent with functional and histological rescue observed in separate RCS rat studies. Given the durability of the ASR chip, ASR implantation may be a treatment option to improve or prolong vision in RP patients. A larger prospective study is appropriate along with investigation of the ASR as possible treatment for other forms of retinal degeneration such as dry AMD.
Keywords: retinal degenerations: hereditary • neuroprotection • retina