Retinal Neurostimulator for a Multifocal Vision Prosthesis

Abstract

A neurostimulator application-specific integrated circuit (ASIC) with scalable circuitry that can stimulate 14 channels, has been developed for an epi-retinal vision prosthesis. This ASIC was designed to allow seven identical units to be connected to control up to 98 channels, with the ability to stimulate 14 electrodes simultaneously. The neurostimulator forms part of a vision prosthesis, designed to restore vision to patients who have lost their sight due to retinal diseases such as retinitis pigmentosa and macular degeneration. For charge balance, the neurostimulator was designed to stimulate with current sources and sinks operating together, and with the ability to drive a hexagonal mosaic of electrodes to reduce the electrical crosstalk that occurs when multiple bipolar stimulation sites are active simultaneously. A hexagonal mosaic of electrodes surrounds each stimulation site and has been shown to effectively isolate each site, increasing the ability to inject localized independent charge into multiple regions simultaneously.

Current Steering in Retinal Stimulation via a Quasimonopolar Stimulation Paradigm

“…To achieve quasimonopolar stimulation, a monopolar (A) and hexapolar (B) configuration must be connected to the stimulator in parallel. Peripheral electrodes (C) do not allow a full ring of guard electrodes to be used, and partial and full hexapolar guards are significantly different at containing charge, 38 so only complete hexes were used. Consequently, the number of stimulating electrodes used in the study was confined to the central 10 electrodes (D).…”

“…The stimulating electrode array was connected through a PXI system (National Instruments Corporation, Austin, TX) to a constant-current stimulator developed in house. The isolated PXI chassis (PXI-1000B) system included a switch matrix (PXI-2532) to redirect the charge-balanced, constant current biphasic pulse, 41 generated by the stimulator, and a digital multimeter (DMM; PXI-4072) to acquire the resulting voltage waveform and determine values for electrode impedance as described by John et al 42 The stimulator contained four constant-current stimulation chips described in Wong et al 38 …”

Current and future prospects for optoelectronic retinal prostheses

“…The Australian Vision Prosthesis Group (AVPG) has designed an epiretinal prosthesis with a similar design to Second Sight, in which power and data are sent to an intraocular implant through a transcutaneous inductive link. 28 A feature of the implant is the unique hexagonal arrangement of electrodes that can assist the localisation of current spread through the neural retina 29 (Figure 4). The AVPG has conducted research into simulation (see below), both internal and external hardware, and animal model experiments.…”

Computational model of electrical stimulation of a retinal ganglion cell with hexagonally arranged electrodes

“…The retinal prosthetic device being developed by our research group has a hexagonallyarranged electrode array, where each active electrode is surrounded by six guards, which collectively return the stimulus current (Hex electrodes). This array design is advantageous in that it isolates each active electrode from M. Abramian neighboring active electrodes and therefore confines the stimulus current to a small area around the center electrode and minimizes electrode cross-talk [6][7][8].…”