Simulation of intra-orbital optic nerve electrical stimulation |
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Authors: | M Oozeer C Veraart V Legat Dr J Delbeke |
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Institution: | (1) Neural Rehabilitation Engineering Laboratory, Universite catholique de Louvain, Brussels, Belgium;(2) CESAME Applied Mechanics, Universite catholique de Louvain, Brussels, Belgium |
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Abstract: | In blind subjects who still have functional retinal ganglion cells, electrical stimuli applied to the optic nerve can produce
localised visual sensations. This has been demonstrated with an intracranially implanted self-sizing spiral cuff electrode,
but, to avoid skull opening, intra-orbital cuff implantation is now considered. In its orbital segment, the optic nerve is
surrounded by subarachnoidal cerebrospinal fluid (CSF) and dura mater. Dura mater is a tough fibrous tissue that can impede
electrical stimulation. In the study, the issue of whether or not to remove the dura mater at the implantation site was addressed
using simulation on numerical models. Several volume conductor models were built representing, respectively: the cuff implanted
directly around the nerve; the cuff over the nerve after connective tissue encapsulated the implant; and the cuff electrode
placed around the dura mater. Stimulation-induced electric potential fields were computed for these configurations using a
full 3D finite elements software. Responses of fibres within the nerve were computed. A large range of dural conductivities
and several CSF thicknesses were considered. In all simulated conditions, the presence of dura mater around a layer of CSF
increased excitation thresholds. Selectivity performance also decreased, but was found to be independent of the CSF thickness.
However, simulations showed that, if the diameter of the cuff electrode is adapted to the target nerve, the injected charge
associated with activation is limited within a reasonable range. Electrical stimulation of the optic nerve with a cuff electrode
implanted around the dura mater should therefore be feasible. |
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Keywords: | Intraorbital optic nerve Cuff electrode Visual prosthesis Finite element method Functional electrical stimulation |
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