Restoration of Sight with Electronic Retinal Prostheses

Retinal prostheses aim at restoring sight to patients blinded by atrophy of photoreceptors using electrical stimulation of the inner retinal neurons. Bipolar cells can be targeted using subretinal implants, and their responses are then relayed to the central visual pathways via the retinal neural network, preserving many features of natural signal processing. Epiretinal implants stimulate the output retinal layer—ganglion cells—and encode visual information directly in spiking patterns. Several companies and academic groups have demonstrated that electrical stimulation of the degenerate retina can elicit visual percepts. However, most failed to consistently and safely achieve an acceptable level of performance. Recent clinical trials demonstrated that subretinal photovoltaic arrays in patients visually impaired by age-related macular degeneration can provide letter acuity matching their 100 μm pixel pitch, corresponding to 20/420 acuity. Electronic zoom enabled patients to read smaller fonts. This review describes the concepts, technologies, and clinical outcomes of current systems and provides an outlook into future developments.