Spatio-temporal characteristics of retinal responses to subretinal photovoltaic stimulation

Abstract

Purpose : To measure the spatio-temporal receptive fields of the retinal ganglion cells activated via subretinal photovoltaic prostheses in degenerate and wild-type rat retinas, and compare them to the natural light responses in healthy retinas.

Methods : Activity of the RGCs was measured in-vitro with a 512 channel multielectrode array. Photovoltaic array with 70µm pixels was placed on the photoreceptor side of healthy and degenerate (RCS) rat retinas. Prosthetic stimulation was performed with 880nm light pulsed at 20Hz and modulated by an LCD displaying binary white noise movies at frame rates of 10Hz and 20Hz. For stimulation of the healthy retina, the same LCD was used to display white noise movies at 30Hz frame rate with continuous visible light illumination. Spatio-temporal receptive fields of the RGCs were measured by calculating the cells’ spiked triggered average (STA) responses to the stimulus.

Results : Significant STA responses to prosthetic stimulation were detected for 10Hz and 20Hz movie frame rates. Prosthetic responses in RCS retinas were classified based on their STAs into two types: eON and eOFF, similar to classification into ON-center and OFF-center types in the healthy retina. The RCS STAs had an average receptive field diameter of 141±11µm and response latency of ~100ms. ON- and OFF-center RGCs in the healthy retina, classified according to their responses to visible light, had response latency of ~180ms. While both ON- and OFF-center RGCs had eON responses to prosthetic stimulation, OFF-center RGCs had half the latency and higher degree of transiency in prosthetic response compared to the ON-center cells. Average receptive field diameter was 239±11µm for visible light and 204±9µm for the prosthetic responses.

Conclusions : Significant prosthetic STA response to white noise movies at 20Hz frame rate indicates that prosthetic vision can operate within a standard range of video frame rates. Spatial receptive fields with prosthetic stimulation in degenerate retinas were smaller than in normal retinas, while these, in turn, were smaller than with natural visual responses in healthy RGCs. Response kinetics were faster with prosthetic stimulation, as expected from the absence of the phototransduction step. Presence of the eON and eOFF responses in the RCS retina demonstrates that prosthetic vision can exhibit some parallel retinal processing even in degenerate retinas.

This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.