Generating Conditions of Focused Virtual Channels Under Simultaneous Electrical Stimulation of Epiretinal Prostheses: A Modeling Study

An epiretinal prosthesis is a promising approach that help patients suffering from retinal degeneration restore partial visual function by activating the surviving retinal ganglion cells. Although some achievements have been made in clinical and commercial practice, a serious problem is that the perceptual resolution of existing prostheses is still low and unsatisfactory. Virtual channels caused by simultaneous dual electrode stimulation (i.e. current steering stimulation strategy) can effectively improve the spatial perceptual resolution of neural prostheses. However, the electric fields produced by current steering stimulation tend to become broader than the single electrode stimulation. To research how to generate the ideal virtual channels, this study focused on investigating the generation conditions of converged electric fields by current steering under epiretinal stimulation. In this study, we calculated theoretically the electrical field profiles in the epiretinal space under different parameters of current steering stimulation, and investigated the relationship among the radius of stimulating electrode, the edge to edge distance between electrodes (EED) and the electrode-retina distance (ERD) that can generate converged single-peaked electric fields. We also found that the convergence of electric fields could be influenced by the ratio of current delivered to the dual stimulating electrodes (defined as stimulation coefficient α), and further evaluated the conditions under which the focused single-peaked electric field could be produced at different α, This study will benefit to the design of appropriate electrode parameters to generate converged virtual channels in epiretinal prostheses.