Computational model of electrical stimulation of a retinal ganglion cell with hexagonally arranged electrodes

Abstract

In retinal prosthetic devices an electrode array is used for electrical stimulation of retinal neurons to induce phosphene perception. The shape and size of the evoked phosphenes are in part dependent on the spatial patterns of retinal activation. In this study, a computational model of a cat beta retinal ganglion cell (RGC) excitation following simulated electrical stimulation was investigated. Seven epiretinal disk electrodes with hexagonal configuration (Hex electrodes) were used. 100 µs/phase anodic-first biphasic pulses were injected at the center electrode and one sixth of the total current was returned at each surround electrode. The aim was to obtain a spatial threshold map of the RGC excitation. We found that the spatial threshold pattern was highly dominated by axonal excitation. With 50 µm Hex electrodes, relative thresholds for activation of the distal axon was almost the same as that for excitation of the axonal trigger segment (high sodium channel density region), causing an elongated activation pattern. The model presented in this study can be used to investigate the extent to which spatial RGC activation patterns are influenced by cell and stimulus parameters.

Chemical stimulation of rat retinal neurons: feasibility of an epiretinal neurotransmitter-based prosthesis

“…In the case of somal RGC stimulation, the receptive field location and hence the visual percept corresponds to the site of stimulation as RGC receptive fields are located close to the somata in the macula region, where retinal prostheses aim to stimulate. However, in the case of axonal RGC stimulation (such as might happen with the Argus II), the corresponding visual percept will often be offset from the site of stimulation [46][47][48]. Our data suggest that eGlu excites somata but not axons (figures 3 and 7), so we expect that with a neurotransmitter-based retinal prosthesis the site of stimulation will always correspond with RGC receptive field locations in visual space.…”

Biomimetic Stimulating Array for Single Localized Stimulation in Visual Prosthesis

“…Recent retinal models [19][20][21][22][23] disregarded a representative three dimensional reconstruction of the ganglion layer for evaluating the direct stimulation of RGCs.…”

“…The layers included in the simulation model are the polyimide carrier of the electrodes, vitreous medium, photoreceptor layer, ganglionic layer, ganglion cell soma and retinal pigment epithelium. This schematic representation of the retina is built to a greater degree of anatomical likeness than previously published works [19][20][21][22][23]. The sizes of each layer and electrical parameters are listed in Table 1 [19][20][21][22][23].…”

“…This schematic representation of the retina is built to a greater degree of anatomical likeness than previously published works [19][20][21][22][23]. The sizes of each layer and electrical parameters are listed in Table 1 [19][20][21][22][23]. The geometric values of the retina are listed in Table 2.…”

A Treatise of the Physical Aspects of Phosphenes and Single-Cell Selectivity in Retinal Stimulation

“…bipolar, horizontal and amacrine cells, ON-and OFF networks) are excluded because of severe rod and cone photoreceptor impairment that cannot drive synaptic connection started with a photocurrent input. The proper conductivity, permittivity and thickness of the layers formerly mentioned can be found in table I [34][35][36][37].…”