A Three-Dimensional Microelectrode Array to Generate Virtual Electrodes for Epiretinal Prosthesis Based on a Modeling Study

Abstract

Despite many advances in the development of retinal prostheses, clinical reports show that current retinal prosthesis subjects can only perceive prosthetic vision with poor visual acuity. A possible approach for improving visual acuity is to produce virtual electrodes (VEs) through electric field modulation. Generating controllable and localized VEs is a crucial factor in effectively improving the perceptive resolution of the retinal prostheses. In this paper, we aimed to design a microelectrode array (MEA) that can produce converged and controllable VEs by current steering stimulation strategies. Through computational modeling, we designed a three-dimensional concentric ring–disc MEA and evaluated its performance with different stimulation strategies. Our simulation results showed that electrode–retina distance (ERD) and inter-electrode distance (IED) can dramatically affect the distribution of electric field. Also the converged VEs could be produced when the parameters of the three-dimensional MEA were appropriately set. VE sites can be controlled by manipulating the proportion of current on each adjacent electrode in a current steering group (CSG). In addition, spatial localization of electrical stimulation can be greatly improved under quasi-monopolar (QMP) stimulation. This study may provide support for future application of VEs in epiretinal prosthesis for potentially increasing the visual acuity of prosthetic vision.

A Patient-Specific Computational Framework for the Argus II Implant

“…Previous retinal stimulation models have been developed using cell physiology data, but with highly idealized FEMs of the implant and surrounding tissue. These models report activation thresholds orders of magnitude lower than clinical research studies [ 14 ]–[ 16 ], [ 31 ], [ 32 ]. By implementing an existing biophysical model into an anatomically realistic FEM, we predict absolute RGC activation thresholds in an amplitude range similar to perceptual thresholds.…”

Computational Modeling of Spatially Selective Retinal Stimulation With Temporally Interfering Electric Fields

“…As shown in Fig. 1, the eyeball model contained several basic structures, including cornea, atria, lens, vitreous body (VB), retina, choroid, and sclera [22], [23]. I listed the parameters [23], [24], [25], [26], [27].…”

“…The steerable electric fields controlled by current ratios without physical electrode movability were similar to the concept of virtual electrodes, which was firstly applied in cochlear implants [30] and utilized for retinal prostheses currently [22], [31], [32]. But unlike the traditional virtual electrodes achieved by direct superposition of the electric field intensity, the movable direction of the interferential electric fields induced by the superposition of various current with different frequencies and amplitudes was closer to electrode pairs with the less output current.…”

“…But unlike the traditional virtual electrodes achieved by direct superposition of the electric field intensity, the movable direction of the interferential electric fields induced by the superposition of various current with different frequencies and amplitudes was closer to electrode pairs with the less output current. However, the traditional virtual electrodes moved closer to the electrode side with a higher output current [22], which can be attribute to distinct principles of the stimulation strategy.…”

Microelectrode Array With Integrated Pneumatic Channels for Dynamic Control of Electrode Position in Retinal Implants

“…In most cases, the outer ring electrode served as a local return to confine the activated RGC region of the center electrode [24,25]. Some studies also showed that a group of ring-shaped electrodes could be used to produce virtual electrodes to enhance visual acuity [26]. The electrode pair design in this work had multiple functions as shown in Fig.…”