Yossi Mandel, Tamar Arens-Arad, Rivkah Lender, Nairouz Farah
School of Optometry and Vision Science, and Institute for Nanotechnology and Advanced Materials (BINA), Bar-Ilan University, Israel.
Purpose: Restoration of central vision in age-related macular degeneration is associated with the intriguing situation where central prosthetic vision co-exists with natural peripheral vision. We studied the effect of the adaptive state of the normal retina on the responses arising from the retinal prosthesis.
Methods: We investigated cortical responses to prosthetic retinal stimulation in wild-type (Long Evans) rats implanted with a 1-mm wide photovoltaic subretinal array. Cortical screw electrodes were implanted over the visual cortex. Cortical responses to prosthetic stimulation elicited by near-infrared (NIR, 910nm) pulses (10ms, 2Hz) of various intensities were recorded in anaesthetized rats following overnight dark-adaption and compared to those following retinal exposure to light (535nm) at various intensities and durations.
Results: Robust cortical responses have been observed in dark adapted rats, exhibiting a sigmoidal increase with the stimuli irradiance. Retinal bleaching by visible light induced a 2-fold decrease in the prosthetic cortical response, which returned to the dark-adapted baseline within 30 min to several hours, depending on the degree of bleaching. This reduction was not observed in rats with degenerated photoreceptors (Royal College of Surgeons, RCS). Similarly, intravitreal injection of a GABAa receptor blocker (biccuculine) abolished the effect of adaptation, suggesting the involvement of GABAa mediated mechanism, potentially operating via the long range amacrine cells inhibition.
Conclusions: These findings suggest the potential effect of the ambient light on prosthetic vision in AMD patients, and may require a careful balance of brightness between the central prosthetic and peripheral natural vision.