| Object:To investigated the surgical procedure, complications, OCT appearance histological changes and the biocompatibllity of the planar and 3D Parylene-based multichannel electrode array in the suprachoroidal of rabbit eyes; investigated the threshold electrical charge density of the retina in rabbits for the generation of electrical evoked potentials (EEP) by delivering electrical stimulation with the planar and 3D Parylene-based multichannel electrode array implanted into the suprachoroidal space.Methods:Part one:1 flat electrode array (parylene plate, platinum electrode) and 1 3D electrode array were developed and used for this study. After performing a scleral incision at 6mm from the limbus and placing an anchoring suture, the array was inserted into the suprachoroidal space in the posterior portion of the eye by direct observation under a microscope,12 adult healthy chinchilla rabbits which were divided in to A group (planar MEA) and B group (3D MEA). The clinical examination including direct ophthalmoscope, and optical coherence tomography were performed in 3day,14 day,1 month and 3 month. The histological examinations were performed at 3month under light microscope.Part two:18 adult healthy chinchilla rabbit were divided in to A group (planar MEA) and B group (3D MEA), the array was inserted into the suprachoroidal space in the posterior portion of the eye. A platinum wire was implanted into the vitreous space as a reference electrode. For electrical stimulation, a biphasic pulse was used. When the electrodes were stimulated, the EEP was recorded. The retinal threshold for generation of an EEP was determined for each MEA placement by consisting of 30 computer-averaged recordings. Animals were sacrificed at the conclusion of the experiment and the eyes were enucleated for histological examination.Results:Part one:All the electrode arrays were successfully inserted into the suprachoroidal space of rabbits. In A group,1 eye the choroid and retina were injured during the surgery.5 eyes in group A and 3eyes in group Bthe choroid were damaged with mild hemorrhage during the surgery. Optical coherence tomography demonstrated good position of the arrays, and no significant retinal edema and retinal detachment were observed. Histological examination showed no significant inflammatory changes in both group. Part two:When the electrical stimulation from the suprachoroidal space was applied, the EEP could be recorded with an epidural electrode, and the average charge threshold of group A was 143.3±27.84 nC, chang density 91.29±17.73 cm-2, maximum charge threshold was 200nC change density 127.39μC cm-2, minimum charge threshold was 120nC, change density 76.43μC cm-2; the average charge threshold of group B was 86.67±18.03 nC, charge density was 55.20±11.48μC cm-2, maximum charge threshold was 120nC, charge density was 76.43μC cm-2, minimum charge threshold was 70μC cm-2,charge density was 44.59 u C cm-2. Histological examination indicated the absence of major damage to the retina and choroid from the insertion place of the array and the electrical stimulation.Conclusion:Suprachoroidal multichannel electrode array insertion is a safe surgery, with little damage to the retina and choroid and no significant inflammatory change after surgery. Transretinal electrical stimulation from the suprachoroidal space could elicit EEP, suggesting that this approach may be useful for a retinal prosthesis system.3D MEA had a lower threshold than planar MEA.
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