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Navya Davuluri, Mark Humayun, James Weiland; Relative efficiency of voltage vs. current pulses for retinal stimulation. Invest. Ophthalmol. Vis. Sci. 2013;54(15):1043. doi: https://doi.org/.
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This in-vivo study is aimed at comparing supra-threshold responses of rat retinal ganglion cells (RGC) to rectangular current controlled and rectangular voltage controlled pulses. This is motivated by the need to determine efficient stimulation strategies for an electronic retinal prosthesis.
In 10 Long-Evans rats, we inserted a Pt/Ir electrode (D= 75 μm) in the left eye and exposed the right SC. The left retina was stimulated with current controlled and voltage controlled pulses of varying pulse width and amplitude. A large needle electrode distant from the eye was used as a current return. While stimulating the retina, evoked potentials were recorded from the superior colliculus (SC), a midbrain structure in the visual pathway. The pulse widths were 0.3 ms, 0.5 ms, 1 ms and 2 ms. For each pulse width, 4 amplitudes between 10 and 60 nC were applied in both current and voltage mode.
Power in the evoked potentials recorded from the SC was used to determine stimulation efficiency. In general, whether current controlled or voltage controlled pulses are more efficient depends on the stimulus pulse width. For 0.3 ms pulse width, at every charge level both current controlled and voltage controlled pulses were equally efficient (student t-test, p > 0.05). For 0.5 ms pulse width, voltage controlled pulses generated evoked potentials with significantly higher power than current controlled pulses (student t-test, p < 0.05). For 1 ms case, current controlled pulses were significantly efficient than voltage controlled pulses for the lower charge levels (student t-test, p < 0.05). And for 2 ms pulse width, current controlled pulses were significantly efficient than voltage controlled pulses for all charge levels (student t-test p < 0.05).
The efficiency of retinal stimulation depends on the pulse width and the stimulation mode. Other factors that may affect stimulation efficiency include electrode size and electrode material.
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