Spatial characteristics of evoked potentials elicited by a MEMS microelectrode array for suprachoroidal-transretinal stimulation in a rabbit

Abstract

Suprachoroidal-transretinal stimulation (STS) can potentially restore vision. This study investigated the spatial characteristics of cortical electrical evoked potentials (EEPs) elicited by STS. A 4 × 4 thin-film platinum microelectrode stimulating array (200 μm electrode diameter and 400 μm center-to-center distance) was fabricated by a micro-electro-mechanical systems (MEMS) techniques and implanted into the suprachoroidal space of albino rabbits. The current threshold to elicit reliable EEPs by a single electrode was 41.6 ± 12.6 μA, corresponding to a 66.2 ± 20.1 μC · cm(-2) charge density per phase, which was lower than the reported safety limits. Spatially differentiated cortical responses could be evoked by STS through different rows or columns of electrical stimulation; furthermore, shifts in the location of the maximum cortical activities were consistent with cortical visuotopic maps; increasing the number of simultaneously stimulating electrodes increased the response amplitudes of EEPs and expanded the spatial spread as well. In addition, long-term implantation and electrical stimulation of the MEMS electrode array in suprachoroidal space are necessary to evaluate systematically the safety and biocompatibility of this approach. This study indicates that the STS approach by a MEMS-based platinum electrode array is a feasible alternative for visual restoration, and relatively high spatial discrimination may be achieved.