Intraretinal stimulation with high density carbon fiber microelectrodes

Retinal prostheses can improve vision for patients blinded by photoreceptor degenerative diseases. Despite the benefits of artificial vision, low spatial resolution of these prostheses limits the positive impact of clinically available devices. Visual percepts generated by single electrodes in epiretinal and subretinal implants can overlap and result in an unclear image, which limits shape and letter perception for retinal prosthesis users. However, research suggests higher resolution may be possible with smaller electrodes implanted intraretinally, in close proximity of target neurons. In this study we used penetrating subcellular-scale carbon fiber microelectrodes for retinal stimulation in an
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vivo mouse retina, and performed calcium imaging to record spatial activation of retinal ganglion cells (RGC) in response to different stimulation amplitudes and RGC-electrode distances. We observed smaller RGC spatial activities and less off-target stimulation with higher RGC-electrode distances, which may be an indication of indirect RGC activation through bipolar cells. Impedance measurements of carbon fiber electrodes demonstrated their mechanical and electrical stability throughout the process of insertion and stimulation. Our results indicate that modification of pulse amplitudes and electrode depths can create small and focal responses around the active electrode. Intraretinal stimulation with carbon fibers can potentially increase stimulation precision and image resolution for retinal prostheses in clinical applications.