Electrophysiological evaluation of a chronically implanted electrode for suprachoroidal transretinal stimulation in rabbit eyes

In this study, we aimed to determine the electrophysiological efficacy, safety, and electrical stability of a chronically implanted electrode for suprachoroidal transretinal stimulation (STS) in rabbit eyes. A platinum microelectrode was implanted into the scleral pocket of rabbit eyes (n = 5) and followed-up for 6 months. To evaluate the electrophysiological efficacy, electrically evoked potentials (EEPs) were measured every month after implantation. To evaluate safety, fundus examinations, fluorescein angiograms, electroretinograms (ERGs), and visually evoked potentials (VEPs) were measured before and every month after the implantation. At the end of the experiment, histological examination of retinal tissue beneath the site of the electrode was performed. To evaluate electrical stability, the resistance of the circuit was measured every month after implantation. EEPs could be elicited from the STS electrodes at all testing times. The mean threshold current to evoke EEPs was 186.4 ± 47.0 µA at 6 months after implantation. There was no significant change in the threshold over the follow-up period. The resistance of the circuit was significantly increased at 1 months after implantation, with no further increase at 6 months. There was no statistically significant change in the relative amplitudes and implicit times of a- and b-waves of ERGs and VEPs. No intraocular infection, inflammation, or vitreoretinal proliferation was observed in any eye. Histological examination revealed no retinal damage beneath the electrode. We conclude that chronically implanted electrodes for STS appear to be effective, safe, and electrically stable.