A light-sensitive, externally powered microchip was surgically implanted subretinally near the macular region of volunteers blind from hereditary retinal dystrophy. The implant contains an array of 1500 active microphotodiodes (‘chip’), each with its own amplifier and local stimulation electrode. At the implant's tip, another array of 16 wire-connected electrodes allows light-independent direct stimulation and testing of the neuron–electrode interface. Visual scenes are projected naturally through the eye's lens onto the chip under the transparent retina. The chip generates a corresponding pattern of 38 × 40 pixels, each releasing light-intensity-dependent electric stimulation pulses. Subsequently, three previously blind persons could locate bright objects on a dark table, two of whom could discern grating patterns. One of these patients was able to correctly describe and name objects like a fork or knife on a table, geometric patterns, different kinds of fruit and discern shades of grey with only 15 per cent contrast. Without a training period, the regained visual functions enabled him to localize and approach persons in a room freely and to read large letters as complete words after several years of blindness. These results demonstrate for the first time that subretinal micro-electrode arrays with 1500 photodiodes can create detailed meaningful visual perception in previously blind individuals.

Subretinal electric stimulation can yield reliable, predictable percepts. Patterned perception is feasible, enabling blind persons to recognize shapes and discriminate different letters. Stimulation paradigms must be optimized, to further increase spatial resolution, demanding a better understanding of physical and biological effects of single versus repetitive stimulation (ClinicalTrials.gov number, NCT00515814).

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Our group has developed a subretinal microphotodiode array for restoration of vision. In a clinical pilot study the array has been implanted in 11 patients suffering from photoreceptor degenerations. Here we present promising results from some of those patients where the retinal tissue above the chip was functional and the implant fulfilled its expected function. A spatial resolution of approximately 0.3 cycles/degree could be achieved with fine stripe patterns. In one subject where the implant had been placed directly under the macular region of the retina a visual acuity of 20/1000 could be measured. Artificially restored visual acuity of this quality has not been reported previously. Finally, we present images illustrating an approximation of how the visual perceptions might have appeared to the subjects, based on a mathematical model and patient reports.

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