3D finite element analysis of the electric field generated by epi-retinal MEMS electrodes

Based on MEMS processing techniques, four different kinds of electrode geometries can be fabricated including concave, flat, convex and coated electrodes. A three-dimensional (3D) multilayered electrode-tissue finite element model was established by means of Comsol Multiphysics 3.5a software. How the different MEMS electrode geometries changed the electric field distributions in the ganglion cell layer surface was studied in this paper. For Φ-300 μm circular electrodes, all the different electrodes including concave, flat, convex and coated ones had charge densities less than the safe charge density limit. Due to the relatively large surface area, the coated electrode produced weak electric field strength less than the threshold value of 1 kV/m. Consequently, the coated one is not ideal for epi-retinal electrical stimulation. The other concave, flat and convex electrodes can be effectively used to electrically stimulate retina tissue axially below the stimulating electrode, and the concave one has some advantages than others: strong and focused electric field strength on GCL layer with low charge density on electrode surface.