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L. Li, M. Sun, P. Cao, X. Chai, K. Wu, X. Sui, Q. Ren; A Visual Prosthesis Based on Intraorbital Optic Nerve Stimulation With Penetrating Electrodes: In vivo Electrophysiology Study in Rabbits. Invest. Ophthalmol. Vis. Sci. 2008;49(13):3037.
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The purpose of this study is to assess the effects of varying stimulus parameters on the electrically evoked potentials (EEP) elicited by intraorbital optic nerve stimulation with penetrating electrodes.
Teflon-coated tungsten wire electrodes were inserted into the intraorbital optic nerve of rabbits. Charge-balanced biphasic current stimuli were applied to the optic nerve via the inserted electrodes. EEP were recorded by epidural electrodes over the visual cortex. The threshold of both current and charge density were determined. The effects of varying stimulus pulse amplitude, duration, frequency and waveform on EEP were studied. Visually evoked potentials (VEP) were recorded as a control. Histological analysis of the optic nerve was performed after the experiments.
EEP were successfully elicited by intraorbital optic nerve stimulation with penetrating electrodes. The threshold of current and charge density for eliciting EEP was 32.08 ± 8.44 µA and 20.99 ± 5.52 µC/cm2, respectively. The P1 amplitude of EEP increased and the latency decreased with increasing current pulse amplitude and duration. The P1 amplitude saturated as the charge was greater than 60 nC. As the stimulus charge was fixed, the P1 amplitude decreased and the latency increased with increment of the pulse duration. The P1 amplitude decreased monotonically when the current frequency varied from 1 to 10 Hz. Among the five different charge-balanced biphasic stimulating waveforms, the symmetrical cathode-first biphasic pulse elicited the largest cortical responses. Histological analysis showed mild damage to the optic nerve tissue induced by the electrical stimulation.
Our study shows that visual prosthesis based on intraorbital optic nerve stimulation with penetrating electrodes requires relatively low thresholds,and narrow symmetrical cathodic-first biphasic pulse with low frequency is more efficient to stimulate the optic nerve directly.
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