Factors Affecting the Efficacy of Retinal Implants

In this study, a realistic rabbit OFF retinal ganglion cells (RGCs) model was utilized with various return electrodes configurations to determine the optimal activation approach for retinal prosthesis. Monopolar and hexapolar return electrode configurations placed epiretinally were utilized. Four types of waveforms were used to deliver the current through the stimulating electrode: biphasic cathodic first, biphasic anodic first, monophasic cathodic, and monophasic anodic pulses. The RGC response was computed at three locations. When the RGC was placed directly below the stimulating electrode, no discernible difference in the required current thresholds for activating RGCs was found between monopolar and hexapolar return electrodes configurations irrespective of the used current stimulus waveform. Moreover, when the RGC was situated remotely, the variation in current thresholds between monopolar and hexapolar was evident. In addition, monophasic anodic was more efficient for monopolar configuration. Additionally, monophasic cathodic stimulation stimulates the RGCs closest to the stimulating electrode.