title: Operational challenges of retinal prostheses.
abstract: Two computational models for research on retinal implants are presented. In the first model, the electric field produced by a multi-electrode array in a uniform retina is calculated. It is shown how cross talk of activated electrodes and the resulting bunching of field lines in monopole and dipole activation prevent high resolution imaging with retinal implants. Furthermore, it is demonstrated how sequential stimulation and multipolar stimulation may overcome this limitation. In the second model a target volume, i.e., a probe cylinder approximating a bipolar cell, in the retina is chosen, and the passive Heaviside cable equation is solved inside this target volume to calculate the depolarization of the cell membrane. The depolarization as a function of time indicates that shorter signals stimulate better as long as the current does not change sign during stimulation of the retina, i.e., mono-phasic stimulation. Both computational models are equally applicable to epiretinal, subretinal, and suprachoroidal vision implants.
authors.affiliation: Institute of Theoretical Physics, Tübingen University, Auf der Morgenstelle 14, 72076 Tübingen, Germany. Electronic address: erich.schmid@uni-tuebingen.de.
authors.forename: Erich W
authors.initials: EW
authors.lastname: Schmid
authors.affiliation: Visual and Autonomous Exploration Systems Research Laboratory, Division of Physics, Mathematics and Astronomy, California Institute of Technology, Pasadena, CA 91125, USA; Visual and Autonomous Exploration Systems Research Laboratory, Departments of Electrical & Computer Engineering, Biomedical Engineering, and Ophthalmology & Vision Science, University of Arizona, Tucson, AZ 85721, USA.
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Fink
authors.affiliation: Krankenhaus Dresden-Friedrichstadt, Dresden, Germany.
authors.forename: Robert
authors.initials: R
authors.lastname: Wilke
mesh_terms: D003198:Computer Simulation; D004558:Electric Stimulation / Q000379:methods; D006801:Humans; D008564:Membrane Potentials / Q000502:physiology; D008954:Models, Biological; D058117:Neural Prostheses; D016012:Poisson Distribution; D012160:Retina / Q000502:physiology*; D055351:Retinal Neurons / Q000502:physiology; D057488:Visual Prosthesis
keywords: Cross-talk; Electric current profile; Electric field profile; Electric field shaping; Electric stimulation; Epiretinal implant; Field line bunching; Phosphenes; Retinal prosthesis; Subretinal implant; Suprachoroidal implant