VISUAL-PERCEPTION ELICITED BY ELECTRICAL-STIMULATION OF RETINA IN BLIND HUMANS

Objective: To evaluate the feasibility of bypassing damaged photorecep tors and electrically stimulating the remaining viable retinal layers to provide limited visual input to patients who are blind because of s evere photoreceptor degeneration. Methods: In the operating room with the patient under local anesthesia, focal electrical stimulation of th e retinal surface with brief biphasic pulses was performed using small probes inserted through the sclera. The procedure was performed in fi ve subjects who had little or no light perception. Three subjects had retinitis pigmentosa, one had age-related macular degeneration, and on e had unspecified retinal degeneration from birth. Results: Stimulatio n elicited visual perception of a spot of light (phosphene). Subjects who previously had useful vision accurately localized the phosphenes a ccording to the retinal area stimulated. Two subjects could track the movement of the stimulating electrode by reporting movement of the eli cited phosphene, and could perceive two simultaneous phosphenes on ind ependent stimulation with two electrodes. In a resolution test, one of the subjects with no light perception in his left eye resolved phosph enes at 1.75 degrees center-to-center distance (ie, 4/200 OS visual ac uity). Conclusions: Local electrical stimulation of the retinal surfac e in patients blind from outer retinal disease results in focal light perception that seems to arise from the stimulated area. Such findings in an acute experiment warrant further research into the possibility of prolonged retinal stimulation, improved resolution, and ultimately, an intraocular visual prosthesis.