Responses of Rabbit Retinal Ganglion Cells to Subretinal Electrical Stimulation Using a Silicon-Based Microphotodiode Array

Abstract

With subretinal prostheses, retinal ganglion cells (RGCs) are activated by electrical stimulation of the retinal neural network. The aim of this study was to evaluate the efficacy of silicon-based solar cells in evoking RGC responses by electrically stimulating the photoreceptor side of an isolated retina. A light-bleached retina of an adult New Zealand White rabbit was placed with its photoreceptor side down onto a silicon chip that consisted of a 4 × 4 microphotodiode array (MPDA). The stimulating current was elicited by activating the solar cell with a 532-nm laser light source. Responses of the ON and OFF alpha RGCs on electrical stimulation were recorded extracellularly. Recorded RGCs were then injected with 4% N-(2-aminoethyl)-biotinamide hydrochloride to allow cell type identification. Using a design that includes a circumvented ground electrode, the authors successfully evoked spiking responses by the ON and OFF alpha RGCs in an isolated rabbit retina using low light power to activate the MPDA (equivalent to 39 μC/cm(2)). The charge density-dependent response and the frequency-dependent pair-pulse suppression were characterized. The spike latency of the RGC responses triggered by electrical stimulation was equivalent to the latency of its light response, which supports the hypothesis that the activation is mediated by the retinal neural network. Reliable activation of RGCs by electrical stimulation in vitro using an MPDA demonstrates the feasibility of developing solar cell-based subretinal prostheses that potentially could be developed into a power-free device able to restore vision.