Experiments were conducted to study if electrical stimulation of the retinal surface can elicit visual sensation in individuals blind from end- stage retinitis pigmentosa (RP) or age-related macular degeneration (AMD). Under local anesthesia, different stimulating electrodes were inserted through the eyewall and positioned over the surface of the retina. Subjects' psychophysical responses to electrical stimulation were recorded. Subjects perceived simple forms in response to pattern electrical stimulation of the retina. A non-flickering perception was created with stimulating frequencies between 40 and 50 Hz. The stimulation threshold was dependent on the targeted retinal area (macular versus extramacular).
Humayun, M. S., De Juan, E., Weiland, J. D., Dagnelie, G., Katona, S., Greenberg, R., & Suzuki, S. (1999). Pattern electrical stimulation of the human retina. Vision Research, 39(15), 2569–2576. https://doi.org/10.1016/S0042-6989(99)00052-8