Abstract
BackgroundEpiretinal prostheses have been greatly successful in helping restore the vision of patients blinded by retinal degenerative diseases. The design of stimulating electrodes plays a crucial role in the performance of epiretinal prostheses. The objective of this study was to investigate, through computational modeling analysis, the effects on the excitation of retinal ganglion cells (RGCs) when different three-dimensional (3-D) electrodes were placed in the epiretinal space.Methods3-D finite element models of retinal electrical stimulation were created in COMSOL using a platinum microelectrode, a vitreous body, multi-layered retinal tissue, and retinal pigment epithelium (RPE). Disk and non-planar electrodes with different 3-D structures were used in the epiretinal electrical stimulation. In addition, a multi-RGC model including ionic mechanisms was constructed in NEURON to study the excitability of RGCs in response to epiretinal electrical stimulation by different types of electrodes. Threshold current, threshold charge density, and the activated RGC area were the three key factors used to evaluate the stimulating electrode’s performance.ResultsAs the electrode-retina distance increased, both threshold current and threshold charge density showed an approximately linear relationship. Increasing the disk electrode’s diameter resulted in an increase in threshold current and a decrease in threshold charge density. Non-planar electrodes evoked different activation responses in RGCs than the disk electrode. Concave electrodes produced superior stimulation localization and electrode safety while convex electrodes performed relatively poorly.ConclusionsInvestigation of epiretinal electrical stimulation using different 3-D electrodes would further the optimization of electrode design and help improve the performance of epiretinal prostheses. The combination of finite element analysis in COMSOL and NEURON software provides an efficient way to evaluate the influences of various 3-D electrodes on epiretinal electrical stimulation. Non-planar electrodes had larger threshold currents than disk electrodes. Of the five types of electrodes, concave hemispherical electrodes may be the ideal option, considering their superior stimulation localization and electrode safety.
Highlights
Epiretinal prostheses have been greatly successful in helping restore the vision of patients blinded by retinal degenerative diseases
We studied the impact of electroderetina distance (ERD) and electrode size on Retinal ganglion cell (RGC) activation
The retina portion consisted of the nerve fiber layer (NFL), ganglion cell layer (GCL), inner plexiform layer (IPL), inner nuclear layer (INL), outer plexiform layer (OPL), outer nuclear layer (ONL), outer segment (OS) of photoreceptors, and retinal pigment epithelium (RPE) (Fig. 1(b))
Summary
Epiretinal prostheses have been greatly successful in helping restore the vision of patients blinded by retinal degenerative diseases. Cao et al Journal of NeuroEngineering and Rehabilitation (2015) 12:73 electrode array in the epiretinal prosthesis is placed on the inner surface of the retina in the macular region, close to retinal ganglion cells (RGCs) [6, 11]. It elicits punctate phosphenes by electrically stimulating the surviving inner retinal neurons (bipolar cells and/or RGCs) to produce artificial vision. A mapping distortion of phosphenes in response to regular electrode array stimulation was reported [16,17,18] This may due to the complicated structure of the human retina. It is important to investigate the responses of RGCs to electrical stimulation
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