Effectiveness of transretinal electrical stimulation using chronically implanted intrascleral electrodes in rabbits

Abstract

Abstract: : Purpose: Previously, we have reported that the transretinal stimulation with the intrascleral electrodes can elicit the electrical evoked potentials (EEPs) in rabbits. In this report, we investigated the effectiveness and the safety of chronically implanted intrascleral electrodes. Methods: A newly developed single channel Platinum (Pt) electrode (<font face="symbol">f</font>0.1mm, convex shape) was introduced into a scleral pocket (3 × 4mm) and secured with the anchoring suture. The epoxy coated Pt wire (<font face="symbol">f</font>0.1mm) was implanted into the corneal stroma as a reference electrode. For electrical stimulation, a biphasic pulse (durations of 0.5 msec for vitreous negative, and 0.5 msec for vitreous positive) was used with various electric currents. Screw–type recording electrode was placed on the skull over the visual cortex. Stimulating and reference electrodes were connected to a socket glued on the skull. EEPs were tested after recording visual evoked potentials (VEPs) up to 3 weeks. The rabbit eyes were enucleated for histological study at 1 month after implantation. Results: The minimum threshold current was 100 uA (50nC). The amplitude and latency of the first positive peak of EEPs with a stimulating current of 300 uA were 15.0 ± 5.0 uV, 23.4 ± 2.5 msec 1 day postoperatively, while 18.8 ± 2.1 uV, 26.6 ± 1.8 msec 3 weeks postoperatively. (N=4). No significant tissue damage was observed around the electrode. Conclusions: EEPs were recorded consistently by a chronically implanted intrascleral electrode with a transretinal current and without significant tissue damage. This data suggest that transretinal electrical stimulation may be safe and useful approach for a retinal prosthesis.

Keywords: retina • retinal development