Stimulation Strategies for Improving the Resolution of Retinal Prostheses

Abstract

Electrical stimulation using implantable devices with arrays of stimulating electrodes is an emerging therapy for neurological diseases. The performance of these devices depends greatly on their ability to activate populations of neurons with high spatiotemporal resolution. To study electrical stimulation of populations of neurons, retina serves as a useful model because the neural network is arranged in a planar array that is easy to access. Moreover, retinal prostheses are under development to restore vision by replacing the function of damaged light sensitive photoreceptors, which makes retinal research directly relevant for curing blindness. Here we provide a progress review on stimulation strategies developed in recent years to improve the resolution of electrical stimulation in retinal prostheses. We focus on studies performed with explanted retinas, in which electrophysiological techniques are the most advanced. We summarize achievements in improving the spatial and temporal resolution of electrical stimulation of the retina and methods to selectively stimulate neurons with different visual functions. Future directions for retinal prostheses development are also discussed, which could provide insights for other types of neuromodulatory devices in which high-resolution electrical stimulation is required.

Photovoltaic retinal prosthesis restores high-resolution responses to single-pixel stimulation in blind retinas

“…The high-density POLYRETINA implant was conceived to offer a large visual angle requiring minimal head scanning and a high resolution through epiretinal network-mediated stimulation, thus overcoming the nerve fibre's direct activation. However, a high pixel density of the prosthesis does not necessarily correlate with high visual discrimination since the response resolution at the retinal ganglion cell (RGC) level might be altered by the high spatial interconnectivity of the retinal network 33,38,39 . Therefore, we investigated ex vivo the response resolution provided by this high-density retinal prosthesis.…”

Human Eye Optics within a Non-Euclidian Geometrical Approach and Some Implications in Vision Prosthetics Design

“…The best acuities reported in the literature so far from clinical trials are 20/1260 from Argus II [ 66 ], 20/546 from Alpha-AMS [ 67 ] and between 20/4451 and 20/21,059 from BVA suprachoroidal devices [ 68 ], all within legal blindness. Crucial abilities, such as facial recognition, are not yet possible [ 69 ]; however, the proposed model is susceptible to lead to a solution for such a problem.…”

Single-pixel epiretinal stimulation with a wide-field and high-density retinal prosthesis for artificial vision

“…When independent pixels stimulate the highly interconnected and spatially organised network of the retina, an increase in the stimulation resolution may not necessarily translate into an equivalent improvement of the RGC response resolution 41,59,36,17 . First, we assessed the RGC RFs under photovoltaic stimulation: 77% of the stimulated RGCs had an average photovoltaic RF diameter slightly larger than the pixels pitch (153.7 ± 26.1 µm), while 23% of the RGCs exhibit a wider photovoltaic RF (335.5 ± 49.3 µm).…”

“…This high-density implant was conceived to offer a relevant resolution for the patient's needs through epiretinal network-mediated stimulation, thus overcoming the direct activation of the nerve fibre layer, and first and foremost a large visual angle with minimal need of head scanning. However, the high pixel density of the prosthesis does not necessarily correlate with a high response resolution at the retinal ganglion cell (RGC) level [39][40][41] , due to the spatial interconnectivity of the retinal network. Therefore, we investigated ex vivo the response resolution provided by this high-density retinal prosthesis.…”