To evaluate the feasibility of bypassing damaged photoreceptors and electrically stimulating the remaining viable retinal layers to provide limited visual input to patients who are blind because of severe photoreceptor degeneration.
In the operating room with the patient under local anesthesia, focal electrical stimulation of the retinal surface with brief biphasic pulses was performed using small probes inserted through the sclera. The procedure was performed in five subjects who had little or no light perception. Three subjects had retinitis pigmentosa, one had age-related macular degeneration, and one had unspecified retinal degeneration from birth.
Stimulation elicited visual perception of a spot of light (phosphene). Subjects who previously had useful vision accurately localized the phosphenes according to the retinal area stimulated. Two subjects could track the movement of the stimulating electrode by reporting movement of the elicited phosphene, and could perceive two simultaneous phosphenes on independent stimulation with two electrodes. In a resolution test, one of the subjects wih no light perception in his left eye resolved phosphenes at 1.75° center-to-center distance (ie, 4/200 OS visual acuity).
Local electrical stimulation of the retinal surface 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.
Humayun MS, de Juan E, Dagnelie G, Greenberg RJ, Propst RH, Phillips DH. Visual Perception Elicited by Electrical Stimulation of Retina in Blind Humans. Arch Ophthalmol. 1996;114(1):40-46. doi:10.1001/archopht.1996.01100130038006