Studies Of The Feasibility, Biocompatibility And Biostability Of Intrascleral Multichannel Electrode Arrays For Visual Prosthesis In Normal Rabbits

Purpose: To estimate the feasibility,biocompatibility and biostability of the intrascleral visual prosthesis, a new polyimide-based multichannel active electrode array was used.Methods: During the first phase, cortical evoked potentials were recorded with implanted epidural electrodes in rabbit during stimulation with light flashes as well as during electrical stimulation in the intrascleral space. After performing the visual evoked potential(VEP) , a 4×4 active electrode array was placed into the intrascleral pocket of the normal rabbit eye. EEP was recorded compared with VEP results. During the second phase, 2 weeks after 1 hour of biphasic pulse stimulation or immediately, the histological findings of the retina in the vicinity of the implant were evaluated, and the scanning electrode microscopies of the electrode arrays were performed.Results: EEP was elicited by the monophasic pulse stimulation. The shape was similar to the VEP. The threshold intensities of the EEP were approximately 10-25nC during cathodic stimulation, and 37.5-75 nC during anodic stimulation. The charge densities were 1×105-2.5×105nC/cm2 and 3.75×105-7.5×105nC/cm2。When electrical intensities were 200μA in the acute experiment and 100μA in the chronic experiment, although the outer segments of retina onto the chip were destroyed, the inner retina was preserved well. But acute electrical stimulation with 500μA and chronic stimulation with 200μA induced severe damage of the retina over the implant, and the top parts of some electrodes were lost.Conclusions: We developed a new, safe approach for placing stimulation chip in the intrascleral space. Suprachoroidal-transretinal stimulation from the intrascleral space could elicit EEP, suggesting that this approach may be useful for a retinal prosthesis system. Data from animal experiments with certain prototypes suggest the safety and probability of the biphasic pulse electrical stimulation with 100μA chronically.