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Yao Chen, Yiliang Lu, Yan Yan, Liming Li, Xinyu Chai; Spatial resolution of the Penetrative Optic Nerve Visual Prosthesis estimated by epidural cortical recording. Invest. Ophthalmol. Vis. Sci. 2013;54(15):1060.
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A visual prosthesis based on penetrating stimulation electrodes within the optic nerve (ON) is a potential way to restore partial functional vision for the blind patients. Although a rough visuotopographic relationship was found between each of the four contacts of the electrode implanted just anterior to the chiasm in the ON by Veraart et al., it is still unknown the topography and spatial resolution of penetrative iON prosthesis implanted close to ON head. In this study, we investigated retinotopic organization of the ON stimulation and its spatial resolution in in vivo cat experiments.
A five-electrode array was inserted perpendicular to the ON axis or a single electrode was advanced at different depths within the ON ~1-2 mm behind the eyeball in 13 cats. Cortical responses were recorded by a 5 × 6 epidural electrode array. A sparse noise method was used to map electrode position in ON and the visual cortex to establish ON and cortical visuotopic maps. Then we compared the visual field positions of ON stimulation sites and their elicited greatest cortical response (M-Channels) sites. Finally, we estimated the spatial resolution of the penetrative ON prosthesis by calculating the difference in M-channel visual field positions corresponding to neighboring ON sites with an inter-electrode distance of 150 μm.
Electrical stimulation with penetrating ON electrodes inserted just posterior to eyeball could elicit cortical responses with visuotopographical correspondence in cats. The electrical stimulation through electrodes within the temporal ON can elicit cortical responses corresponding to the central visual field. According to the increment of penetrating depth, the corresponding elicited cortical responses shift from lower to central visual field. About 2° to 3° spatial resolution within a limited visuotopic representation in the cortex could be obtained by this approach.
Visuotopic electrical stimulation with relatively fine spatial resolution could be accomplished by penetrative electrodes implanted at multi-sites and different depths within ON close to the optic nerve head. This study also provided useful experimental data for the design of electrode density and distribution of penetrating ON electrodes for a visual prosthesis.
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