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Optimization of Electrical Stimulus Pulse Parameter for Low-Power Operation of Retinal Prosthetic Device

In this paper, we describe the investigation of an electrical stimulus pulse parameter for use in a low-power retinal prosthesis. To obtain efficient stimulus pulse parameters, in vitro electrical stimulus experiments with a detached frog retina were performed using a fabricated pulse-frequency modulation (PFM) image sensor as a retinal prosthesis. The evaluated electrical stimulus pulse parameters were pulse duration, pulse amplitude, and the number of pulses. From the experiments, the firing rate of the retinal ganglion cells (retinal ganglion cells; RGCs) was observed to depend on the injection charge in single-pulse stimulation and the injection charge of the first pulse in pulse-train stimulation. In addition, pulse-train stimulation was found to have a RGC firing rate lower than that of single-pulse stimulation at the same injection charge. From power consumption measurements and an in vitro experiment, it was verified that the stimulus pulse of a short-pulse duration is suitable for use in a low-power retinal prosthesis.