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U.S. Department of Health and Human Services

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Research Project: Safety of Electrical Stimulation in the Retina

Principal Investigator: Ethan Cohen

FDA collaborators: Anant Agrawal and Joshua Pfefer.

Collaborators: Nathalia Peixoto, Hamid Charkhkar, and Saugandhika Minnikanti, George Mason Univ.

Retinal prostheses seek to stimulate the degenerated retinal network in visually impaired patients to elicit a sensation of light termed a “phosphene”. Little is known about what levels of electrical stimulation are safe for the retina. The objective of this project is to determine safer and more effective methods of nerve cell stimulation. We use the retina, a CNS-derived piece of neural tissue as a model system. Using optical, physiological, bioimpedance, and computational methods, we are determining the safety of electrical stimulation for activating the neurons in the retinal network. We are currently measuring the resistivity and permittivity of the tissue layers forming the rabbit eye wall. In a collaboration with the Peixoto lab (George Mason Univ), this has allowed us to predict the propagation of the electric field by stimulus electrodes. We have also developed a novel optical coherence tomography method to observe neurons directly under a transparent stimulation electrode during pulse train stimulation. Retinal tissue swelling and layer deformation can now be observed during stimulation in real time. The results of this project will provide FDA with a better understanding of how the retinal layers are activated by electrical stimulation pulses and help determine what levels of electrical stimulation are safe for retinal tissue.


Schematic diagram of a typical retina-based visual prosthesis showing the different proposed locations for the stimulation electrodes (red discs) in the eye  The retina and optic nerve are shown in blue.


Spectral-domain optical coherence tomography B-scan (cross sectional image) of the live rabbit eye wall directly under a transparent stimulation tube. Note the image of the retina is undistorted even under the walls of the stimulation tube.