Abstract
Our goal was to determine the feasibility of using electrochemically treated bulk platinum electrodes with large charge injection capacity for a retinal prosthesis. Seven eyes of seven cats were studied. Small retinal areas were focally stimulated with electrochemically treated bulk electrodes (φ=500µm) placed in a scleral pocket. Fundus images with near-infrared (800-880nm) light were recorded, and a 2D map of the reflectance changes elicited by the electrical currents was constructed by subtracting the images taken before stimulation from those taken after stimulation. The impedance of each electrode was measured at 1kHz. The degree of retinal elevation by the electrode was measured by optical coherence tomography. Scleral thickness where the electrode array was inserted was measured in histologic sections. The diameter of reflectance changes (full width at half maximum) was 0.42±0.22mm [mean±standard deviation (SD)] in minor axes and 1.46±0.82mm in major axes. The threshold current decreased with a reduction in the residual scleral thickness (R (2)=0.9215; P=0.0002); it also decreased with an increase in retinal elevation (R (2)=0.6259; P=0.0111).The threshold current also decreased with an increase in electrode impedance (R (2)=0.2554; P=0.0147). Electrochemically treated porous platinum electrodes can stimulate localized retinal areas. The threshold current necessary to stimulate the retina was influenced by residual scleral thickness and the electrode tightness of fit against the sclera.
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