Abstract
Background and Aims:
Retinal prostheses have been suggested to restore vision for those with retinal diseases. This study aimed to identify the most effective stimulation approaches for retinal prostheses.

Methods:
This study examined various return electrode configurations on a realistic retinal ganglion cell model. Two return electrode configurations, monopolar and hexapolar, were implanted on epiretinal side. There were four waveforms used to send electrical current through the active electrode. The study also compared two stimulation methods: single stimulation and concurrent (parallel) stimulation.

Results:
Directly placing the retinal ganglion cell beneath the active electrode resulted in no significant difference in the required current for stimulating retinal ganglion cells between monopolar and hexapolar return electrodes, regardless of the stimulation waveform. For retinal ganglion cells located away from the active electrode, differences in the required current were noted between the two return electrode configurations. The study discovered that parallel stimulation with two or three active elec¬trodes lowered current requirements by up to 70% compared to single stimulation. Monophasic anod¬ic stimulation yielded the most effective pulse waveform, regardless of the configuration (monopolar or hexapolar) or stimulation mode (single or parallel). Moreover, monophasic cathodic stimulation usually targets retinal ganglion cells around the active electrode.

Conclusions:
These results illuminate the best stimulation strategies for enhancing the efficacy of retinal prosthe¬sis. The study highlights the importance of electrode arrangement, waveform selection, and single or concurrent stimulation for improving retinal ganglion cell activation.

Key words: RGC, Monopolar, Hexapolar, Single Stimulation, Concurrent Stimulation, Pulse waveform