Andrew Grumet's Master's Thesis

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Citation information: Grumet, Andrew E. Extracellular Electrical Stimulation of Retinal Ganglion Cells. Master's Thesis, Massachusetts Institute of Technology, 1994.


The research conducted for this thesis was part of an overall effort to develop a retinal prosthesis to aid blind patients suffering from disease of the photoreceptors. We hope to restore vision to such patients by implanting a device which electrically stimulates the healthy cells of the inner retina. Preliminary experiments indicate that the threshold amounts of current required to stimulate retinal ganglion cell bodies and axons typically fall within the same range. We believe that stimulation of ganglion cell axons will hinder our ability to elicit phosphenes of discernible resolution in implanted patients. For this reason, current research efforts are directed in part at finding a way to stimulate retinal ganglion cell bodies without exciting the axons which overlie them at the innermost layer of the retina.

The goal of this thesis is to design a stimulating electrode which employs a novel geometry to selectively stimulate retinal ganglion cell bodies. Discussions of the retina and of the retinal prosthesis are provided at the outset of the thesis. Simple models of nerve cells are then constructed and analyzed both to guide the design process and also to develop a general understanding of electrical stimulation. Analysis leads to the specification of a new experimental electrode and a description of how it was constructed. A description of preliminary experiments which were conducted to test the electrode follows. Due to a number of unresolved experimental issues, experimental results were inconclusive. Suggestions for further study are made in the concluding chapter of the thesis.