AnIn VitroModel of a Retinal Prosthesis

Abstract

Epiretinal prostheses are being developed to bypass a degenerated photoreceptor layer and excite surviving ganglion and inner retinal cells. We used custom microfabricated multielectrode arrays with 200-μm-diameter stimulating electrodes and 10-μm-diameter recording electrodes to stimulate and record neural responses in isolated tiger salamander retina. Pharmacological agents were used to isolate direct excitation of ganglion cells from excitation of other inner retinal cells. Strength-duration data suggest that, if amplitude will be used for the coding of brightness or gray level in retinal prostheses, shorter pulses (200 μs) will allow for a smaller region in the area of the electrode to be excited over a larger dynamic range compared with longer pulses (1 ms). Both electrophysiological results and electrostatic finite-element modeling show that electrodeelectrode interactions can lead to increased thresholds for sites half way between simultaneously stimulated electrodes (29.4 ± 6.6 nC) compared with monopolar stimulation (13.3 ± 1.7 nC, p < 0.02). Presynaptic stimulation of the same gan-glion cell with both 200-and 10-μm-diameter electrodes yielded threshold charge densities of 12 ± 6 and 7.66 1.30 nC/cm 2 , respectively, while the required charge was 12.5 ± 6.2 and 19 ± 3.3 nC.

Electrically-evoked Neural Activities of rd1 Mice Retinal Ganglion Cells by Repetitive Pulse Stimulation

“…RGC responses to repetitive stimulation pulses have been reported for normal retinas (Fried et al, 2006;Sekirnjak et al, 2006;Jensen and Rizzo, 2007;Ahuja et al, 2008). However, few reports have described RGC responses of degenerated retinas evoked by repetitive pulse stimulations.…”

Response variability to high rates of electric stimulation in retinal ganglion cells

“…The temporal properties of light-elicited patterns can vary considerably across types, suggesting that the prosthetic must be able to create a similarly wide range of temporal responses, including high-frequency bursts of spiking used by some cell types. Previous studies that have explored the temporal responsiveness of retinal ganglion cells have shown that a single, short-duration (ϳ0.1 ms) stimulus pulse elicits a single action potential that is phase-locked to the onset of the cathodal pulse (Ahuja et al 2008;Fried et al 2006;Sekirnjak et al 2006). In this manner, trains of short-duration pulses have been shown to elicit trains of action potentials.…”

The Effect of Return Electrode Position on Induced Electric Fields for Electrical Stimulation of Retinal Ganglion Cells

“…Differential equations that describe and solve the problem are presented. Electric field behavior produced by electrical stimulation of the tissue is stated using the Maxwell equations and its derivatives [6][7][8][9][10][11]. Electric field is calculated by solving the Maxwell equations under quasi-static conditions…”