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LJ Johnson, FK Perkins, C Merritt, P Skeath, B Justus, J Weiland, M Humayun, D Scribner; Low Charge Density Stimulation Of Isolated Retina With Microchannel Glass Electrodes . Invest. Ophthalmol. Vis. Sci. 2002;43(13):4480.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: We hypothesize that curved microchannel glass with microwires can be used as an interface between a flat 3200 electrode intraocular retinal prosthesis chip and the retina. Furthermore, we expect that the retina can be stimulated with microchannel glass with microwires at current and charge levels that do not damage the retina (<100 micro Coulombs/cm2). Method: We performed electrical stimulation experiments on isolated rabbit retinas (n=6). The extracellular potential was measured with a differential amplifier to evaluate the retinal response to stimulation with a 2.4mm2 microchannel glass electrode. A series of biphasic current pulses were delivered with a range of pulse durations from 0.1ms to 4 ms, 3ms interphase delay. The current ranged from 1.66mA to 0.17mA. The current threshold for spike generation was found for each pulse duration. In some experiments we stimulated with smaller electrodes of area less than 0.16mm2. Results: The extracellular response of the retina was found to consist of multiple action potentials, or spikes, in two distinct populations, early and late. The early spikes typically occurred within 50 ms of the pulse onset. We found that the threshold for spike generation decreased with increasing pulse duration and the number of spikes evoked at threshold increased with increasing pulse duration. However, when taking into account the charge delivered and the power consumed for each early spike generated at threshold, the optimal pulse duration appears to be between 0.5 and 0.9ms. For the 0.9ms pulse, 7±5 spikes per mA were generated at a threshold of 0.75±0.31 mA, delivering 31.1 micro Coulombs/cm2. Our smaller electrode required less current and charge density (0.06±0.03mA, 1.7 micro Coulombs/cm2) to generate spikes. Conclusion: Channel glass electrodes are capable of stimulating the retina at safe levels. Preliminary results show that smaller channel glass electrodes, at the ganglion cell layer, require less overall current to generate spikes but a higher current density. However for smaller electrodes, there is a decrease in the charge density required for stimulation.
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