Optimizing Electrical Stimulation Parameters to Enhance Visual Cortex Activation in Retina Degeneration Rats

In patients with degenerative diseases of the retina, such as retinitis pigmentosa and age-related macular degeneration, retinal prostheses offer a possible method of restoring partial vision. Epiretinal prosthesis remain the need for optimal stimulation parameters for better efficiency and power saving while showing encouraging preliminary clinical efficacy. In this study, we investigate the effects of retinal electrical stimulation parameters, including phase duration, frequency, and interphase interval, on the visual cortical electrically evoked potentials (EEPs) in both healthy (LE) and retinal degenerated (F1) rats. Our in vivo experiments on both LE and F1 rats suggest that shorter phase durations (500 μs) activate the primary visual cortex (V1) at a lower charge threshold and result in a larger activated area. Our results also show that response to repetitive stimulation decreases profoundly at high frequencies (10 and 20 Hz) compared to low frequency (1 Hz). Additionally, we observe that the inclusion of an interphase interval enhances the level of cortical response but does not contribute to an increase in the activation ratio. The present work suggests epiretinal stimulation using shorter phase durations without interphase intervals as the optimal strategy to safely activate the target region in V1 in both LE and F1 rats.