Retinotopic Responses in the Visual Cortex Elicited by Epiretinal Electrical Stimulation in Normal and Retinal Degenerate Rats.

PURPOSE

Electronic retinal prostheses restore vision in people with outer retinal degeneration by electrically stimulating the inner retina. We characterized visual cortex electrophysiologic response elicited by electrical stimulation of retina in normally sighted and retinal degenerate rats.

METHODS

Nine normally sighted Long Evans and 11 S334ter line 3 retinal degenerate () rats were used to map cortical responses elicited by epiretinal electrical stimulation in four quadrants of the retina. Six normal and six rats were used to compare the dendritic spine density of neurons in the visual cortex.

RESULTS

The rats required higher stimulus amplitudes to elicit responses in the visual cortex. The cortical electrically evoked responses (EERs) for both healthy and rats show a dose-response characteristic with respect to the stimulus amplitude. The EER maps in healthy rats show retinotopic organization. For rats, cortical retinotopy is not well preserved. The neurons in the visual cortex of rats show a 10% higher dendritic spine density than in the healthy rats.

CONCLUSIONS

Cortical activity maps, produced when epiretinal stimulation is applied to quadrants of the retina, exhibit retinotopy in normal but not rats. This is likely due to a combination of degeneration of the retina and increased stimulus thresholds in , which broadens the activated area of the retina.

TRANSLATIONAL RELEVANCE

Loss of retinotopy is evident in rats. If a similar loss of retinotopy is present in humans, retinal prostheses design must include flexibility to account for patient specific variability.