Switching of return electrodes improve the efficiency of supracholoidal-transretinal electrical stimulation in artificial retinae.

Abstract

Purpose : The efficiency of electrical stimulation to retinae is essential in retinal prostheses, which send visual information to blind patients via electrical stimulation of the visual system. Previous studiy suggested that the threshold of anodal monophasic pulse was lower than that of biphasic pulse in subretinal stimulation (Jensen et al., IOVS 2009). This study aims to investigate whether sequential switching of two return electrodes during biphasic pulse, which cause monophasic-like current transient in the retina, can increase neural responses.

Methods : Nine Royal College of Surgeons (RCS) rats were used in this study. A stimulating electrode was placed on the sclera of the eye. Two return electrodes, the proximal return and the distal return, were employed. The proximal return electrode was placed adjacent to the stimulating electrode, and the distal return electrode was placed under the skin of the rats' noses. Cathodic-first charge-balanced 500-μs-width biphasic pulses were applied to the retina. Current pulses were applied between the stimulating and proximal return electrodes in the first phase of biphasic pulse; then, the return electrode switched from the proximal to the distal return for the second phase (Fig. 1B). Electrically evoked potentials (EEPs) were recorded by a needle electrode placed in the superior colliculus of the rat. All experiments were conducted in accordance with the Association for Research in Vision and Ophthalmology statement for the use of animals in ophthalmic and vision research with the approval of the institutional Animal Care and Use Committee of NIDEK CO., LTD.

Results : Amplitudes of EEPs induced by biphasic pulses with return-switching were significantly greater than those without return-switching (Fig. 1A, only the distal return electrode was used during stimulation) when the current amplitude of stimulation was close to the thresholds (paired t-test, p<0.01 at 50 μA, p<0.05 at 100 μA). On the other hand, no significant differences in EEP amplitudes were observed when stimulation intensities were relatively large.

Conclusions : Results suggested that switching return electrodes during electrical stimulation affects stimulation efficacy. We will further study to quantify the increase of EEP amplitude and investigate the underlying mechanism.

This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.

 

Fig.1 Biphasic pulse without return-switching (A) and with return-switching (B).