Focal activation of the feline retina via a suprachoroidal electrode array

This paper presents the results of the first investigations into the use of bipolar electrical stimulation of the retina with a suprachoroidal vision prosthesis, and the effects of different electrode configurations on localization of responses on the primary visual cortex. Cats were implanted with electrodes in the suprachoroidal space, and electrically evoked potentials were recorded on the visual cortex. Responses were elicited to bipolar and monopolar stimuli, with each stimulating electrode coupled with either six-return electrodes, two-return electrodes, or a single-return electrode. The average charge threshold to elicit a response with bipolar stimulation and six-return electrodes was 76.47+/-8.76 nC. Bipolar stimulation using six-return electrodes evoked responses half the magnitude of those elicited with a single or two-return electrodes. Monopolar stimulation evoked a greater magnitude, and area of cortical activation than bipolar stimulation. This study showed that suprachoroidal, bipolar stimulation can elicit localized activity in the primary visual cortex, with the extent of localization and magnitude of response dependent on the electrode configuration.