In vivo evaluation of an episcleral multielectrode array for stimulation of the retina with reduced retinal ganglion cell mass

A visual prosthesis is an experimental device designed to activate residual functional neurons in the visual pathway to generate artificial vision for blind patients. Specifically, for photoreceptor disease, a microelectrode array applied to the surface of the sclera could potentially serve to stimulate the remaining interneurons in the retina to produce topographically mapped visual percepts. However, of those neurons spared in the disease process, the retinal ganglion cells (RGC), which represent the final output neurons of the retina, can be markedly reduced in number. Using an albino rabbit model with RGC deficits, acute recording of cortical electrical evoked potential was performed to ascertain whether such a stimulation strategy is feasible. By analyzing the strength-duration curve (current threshold vs. pulse duration) and cortical activation profiles, our results prove that bioelectrically safe and spatially differentiated stimulation of the retina is feasible notwithstanding the condition of markedly reduced RGC counts.