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Yukari Nakano, Yasuo Terasawa, Hiroyuki Kanda, Motoki Ozawa, Hajime Sawai; The effect of an asymmetric pulse in retinal prosthesis based on suprachoroidal-transretinal stimulation (STS). Invest. Ophthalmol. Vis. Sci. 2017;58(8):4176. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
To find out more effective electrical stimulation parameter, we examined the effect of an asymmetric pulse in suprachoroidal-transretinal stimulation (STS).
Normal rats (Long–Evans, n = 3) anesthetized with urethane (1.75 g/kg) were used for the acute electrophysiological experiments. A platinum stimulating electrode (diameter, 0.5 mm; height, 0.3 mm) and a return electrode (22 G needle) were positioned in the partial scleral resection of the eyeball and in the subcutaneous tissue of the nose, respectively. A single symmetrical biphasic pulse (anodic first [AF] or cathodic first [CF]) of constant current with 0.5 ms of phase duration was applied between the electrodes as a control stimulation to record evoked field potentials (EPs) from the superior colliculus. The amplitudes of the EPs were compared with those to an asymmetric biphasic pulse, of which the duration of the anodal phase or cathodal phase was extended four times (2 ms) with the same amount of electric charge.
In both AF and CF electrical stimulation, the mean amplitudes of EP significantly decreased as longer duration of the anodal phase, irrespective of AF or CF pulses (AF, 520 ± 170 µV vs. 111 ± 73 µV, p<0.05, CF, 550 ± 154 µV vs. 215 ± 132 µV, p<0.05, Mean ± SD, Symmetric vs. Asymmetric, paired t-test). In contrast, extension of the cathodal phase did not result in a reduction of EP amplitudes (AF, 520 ± 170 µV vs. 506 ± 157 µV, p = 0.24, CF, 550 ± 154 µV vs. 574 ± 177 µV, p = 0.24, paired t-test).
It is demonstrated that the anodal phase in a biphasic pulse of suprachoroidal stimulation excite visual cortical neurons more effectively than cathodal phase does [John et al. J. Neural Eng. 2013]. Our results confirm the previous study and suggest that shorter duration and higher current of anodal pulse can be more effective to evoke a large EP to an asymmetric biphasic pulse.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.
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