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Subretinal electronic chips can restore useful visual functions in blind retinitis pigmentosa patients

Retinitis pigmentosa leads to progressive loss of retinal photoreceptors causing blindness. We developed an active subretinal electronic device being implanted in 11 volunteers suffering from a hereditary retinal disease in an end-stage. The active part of the implant consists of a chip carrying a microphotodiode array (MPDA) with 1500 light sensitive pixels and of a 4 x 4 matrix of electrodes for direct retinal stimulation and assessment of the tissue-electrode interface. The direct stimulation of the retina was performed by single electrodes or patterns formed by the 4x4 matrix leading to percepts described as well defined dots. Stimulation by simple patterns could be reliable recognized and described in tested subjects. Five of the eleven patients could use the subretinal MPDA to perceive and localize light sources or large bright objects. In two subjects spatial resolution up to 0.32 cycles/deg and 0.22 cycles/deg was achieved. In the subject, whose subretinal implant has been placed directly under the macula a visual acuity of 20/1000 could be measured by a standard test, as well as letters and words recognition. For the first time we could show that subretinal implants can restore useful visual functions in blind patients with hereditary retinal diseases.