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P. A. Degenaar, N. Grossman, B. McGovern, R. Berlinguer-Palmini, M. Neil, E. Drakakis; Photogenetic Retinal Prosthesis. Invest. Ophthalmol. Vis. Sci. 2009;50(13):3899.
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Retina dystrophies such as age-related macular degeneration (AMD) and retinitis pigmentosa (RP) are a major cause of blindness in most of the developed countries. There is no effective rehabilitation treatment for these diseases today. The ability to return phosphenes to blind patients via electronic prosthesis has been improving with better electronics and neural interface materials. However, resolution is poor, and the inability to inhibit neural firing could prove to be a significant limitation. In our approach we genetically re-engineer the retinal ganglion cells to be light sensitive and have been developing an optoelectronic stimulator system to return functional vision.
We have induced photosensitivity into both cultured and in-vivo neurons via transfection with the light sensitive ion channel Channelrhodopsin-2 (ChR2). In culture we have used electroporation and lipofectamine methods of gene transfer and in-vivo we have used AAV-2 vectors. We have performed a biophysical characterization of the photokinetics of ChR2 from which we have developed parameters to design our electronics system.
We developed an in-vitro prototype using custom fabricated microLED’s and investigated its spatiotemporal resolution. We can demonstrate individual cell and subcellular targeting. Also, it is capable of illuminating the neurons with sufficient brightness (100mWcm-2) and speed (>1KHz per pixel) to achieve action potential image transfers. In addition we have investigated the light intensity requirements and believe it is possible to illuminate sufficient numbers of LED’s to provide an interpretable visual scene without exceeding photochromic damage thresholds.
Advances in biochemistry have allowed us to impart photosensitivity to retinal ganglion cells. Further advances will allow targeting of specific cells and even subcellular components. In parallel, we have been developing the optoelectronic equipment to return functional vision to the user.Figure : The proposed neuroprosthetic system. (Left) A conceptual design of our final system. (Right) The engineering pathway(top) and the results to date (bottom).
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