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Sheila N. Nirenberg, Chethan Pandarinath; A Retinal Prosthetic Approach with the Capacity to Restore Normal Vision. Invest. Ophthalmol. Vis. Sci. 2011;52(14):4932.
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Retinal prosthetics are still very limited in the vision they provide. Patients are able to see spots of light and high contrast edges, which provide some ability for navigation and gross feature detection, but nothing close to normal vision has been possible. Efforts to improve prosthetic performance have focused largely on increasing the resolution of the devices’ stimulators. But a second factor is also critical: driving the stimulators to produce normal retinal output, that is, output in the retina’s neural code. Here we focus on the latter and measure the impact this has on prosthetic capabilities.
We generated a prosthetic system that consists of two parts: an encoder and a transducer. The encoder converts visual input into the code used by the ganglion cells, and the transducer then drives the ganglion cells to fire as the code specifies. We constructed the prosthetic in a mouse model of retinal degeneration using an optogenetic transducer (channelrhodopsin-2 (ChR2)). We then compared the capabilities of this system with the standard optogenetic system, i.e., just the transducer, ChR2.
The results showed that including the code dramatically increased the system’s capabilities, well beyond what could be achieved by increasing resolution alone. Furthermore, they showed, using 6000 optogenetically-stimulated mouse ganglion cell responses, that the combined effect of using the code and high-resolution stimulation was able to bring prosthetic capabilities into the realm of natural vision: there was enough information in the system's output to discriminate a broad range of spatio-temporally varying scenes and to reconstruct images including faces, animals, and landscapes.
These findings provide strong evidence that the key components for addressing the retinal prosthetic problem are now, to a large extent, in place - at least for the mouse test case. The coding strategy, teamed with a high resolution transducer, optogenetic or electronic, opens the door to a new level of vision restoration. Furthermore, the results emphasize the direct impact of basic research to applied/clinical problems.
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