Comparison of voltage parameters for the stimulation of normal and degenerate retina

Retinal prosthesis is regarded as a promising method for restoring vision for the blind with retinal diseases such as retinitis pigmentosa (RP) and age related macular degeneration (ARMD). Among the several prerequisites for retinal prosthesis to succeed, one of the most important is the optimization of electrical stimuli applied through the prosthesis. Since the electrical characteristics of diseased retina are expected to be different with those of normal retina, we investigated different voltage parameters to stimulate normal and degenerate retina. The retinal degeneration model (rd/rd mouse) was compared against control mice. Voltage stimulations were delivered via one channel of 60 channels 8 x 8 Multi-electrode array (MEA), and ganglion cell activities were recorded with the remaining 58 channels. The parameters of voltage stimulation were set based on previous experiment with rabbit. Evoked ganglion cell responses were counted during a 10 - 20 ms time span after the stimulation. The voltage amplitudes and voltage durations were set to obtain consistent values for ganglion cell responses. When the same stimulus was applied on the rd/rd mouse, evoked ganglion cell responses were rarely observed. The distribution patterns of evoked responses appeared only on a site distant from the stimulation electrode on the rd/rd retina. Conversely, in normal retina, evenly distributed response patterns were observed. Since the charge intensity tends to decrease with the distance from stimulation electrode, the uneven patterns from the rd/rd mouse retina suggest that lower charge is required to evoke a response from rd/rd retina.