Cortical response to combined prosthetic and visible stimuli exhibits similarities to natural visual processing

Abstract

Purpose : Prosthetic restoration of central vision in age-related macular degeneration (AMD) involves a combination of prosthetic vision in the central macula along with natural vision in the periphery. Here we study cortical interaction of visible and prosthetic stimuli, which is of great clinical and scientific importance.

Methods : Subretinal implantation of 1mm-diameter photovoltaic arrays in wild-type rats induced a localized degeneration of the photoreceptors above the implant, whereas the surrounding retina was left intact, similar to the localized retinal degeneration caused by AMD. Using a customized projection system, we induced prosthetic and natural visual responses with NIR (910nm) and visible light (532nm), respectively. Each presentation was comprised of a central 1mm prosthetic or visible stimulus encircled with a 3mm visible surround. We recorded visual evoked potentials (VEP) in response to either non-patterned (flash or contrast step) stimuli or to complex grating patterns.

Results : Responses for both visible and prosthetic flash stimuli were reduced by increasing a continuous visible light background. Combined prosthetic and natural non-patterned stimuli (flashes and contrast steps) exhibited a simple cortical linear summation. In contrast, responses to alternating-grating targets composed of either visible or prosthetic central area surrounded by visible grating flankers revealed significant lateral inhibition phenomenon. For both prosthetic and visible targets, lateral inhibition increased with the target contrast, reaching a maximum inhibitory effect of 40%.

Conclusions : The observed striking similarities between cortical responses to patterned natural illumination and to combined prosthetic-natural stimuli suggest that basic processing interactions are preserved when a combined information is presented to the visual cortex. These results are an important step for understanding the cortical processing of the combined prosthetic and natural vision and can aid in prosthetic restoration of central vision in AMD patients.

This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.