Continuous electrical stimulation decreases retinal excitability but does not alter retinal morphology.

Retinal prostheses aim to provide visual perception through electrical stimulation of the retina. Hence they have to operate between threshold charge density and maximum safe charge density. To date most studies in the retina have concentrated on understanding the threshold, while stimulation safety has predominantly been studied in structures other than the retina. Toward this end, the present study focuses on determining the effect of continuous electrical stimulation of the retina both on retinal morphology and on the electrically evoked responses in the superior colliculus in a rodent model. The results demonstrate that the retina is able to tolerate 1 h long stimulation with only minor changes evident in retinal histology when examined three to 14 days later, even at charge densities (0.68 mC cm(-2)) above the safe limit of platinum delivered at high stimulus frequency (300 Hz). However, this continuous electrical stimulation causes an elevation in the threshold of the electrically evoked response in the superior colliculus, indicating some form of adaptation to continuous stimulation.