Comparison Between The Epiretinal And Subretinal Implantation Of The Polyimide Electrode Array For The Electrical Stimulation Of The Retina

Abstract

Purpose: : To investigate the usability of the polyimide electrode array for the retinal prosthesis system, epiretinal or subretinal implantation techniques are developed and the biocompatibility was tested.

Methods: : To prevent tearing of edge, polyimide microelectrode array is designed to have rounded corners and circular holes for retinal tack. The electrode array is 18.5µm in thickness and 3 x 3 mm in size. Each gold electrode is 200 x 200µm in size and is spaced by 250µm. To fix the electrode array onto the retina, silicon retinal tack was designed and manufactured by MEMS technology. For the epiretinal implantation of the electrode array, lens–sparing 3 port pars plana vitrectomy was done in white rabbits under general anesthesia. After vitrectomy, electrode array was curled and inserted into the eyeball through sclerotomy site. It was fixed onto the retina with silicon retinal tack. Sclerotomy site and conjunctiva were repaired with 8–0 vicryl suture. For the subretinal implantation, electrode array was introduced under the subretinal space via transscleral approach without vitrectomy. Stimulating electrode was located near the visual streak of posterior pole and the connection site was kept on the external surface of the sclera. During the follow–up period, regular indirect ophthalmoscopic examination was done to evaluate the inflammatory changes or other complications in vitreous and retina. The histological change of retina was also evaluated.

Results: : Indirect ophthalmoscopic examination revealed that polyimide microelectrode array had not induced haziness or inflammatory change of vitreous for 2 years after the operations. Dissection of eyes also certified that there was no retinal detachment, vitreous haziness, cataract changes in both implantation techniques. There was no displacement of epiretinally fixed polyimide microelectrode array or subretinally implanted array during follow–up period. Microscopic exam revealed fibrous encapsulation around the silicon retinal tack at the external portion to the sclera.

Conclusions: : Both epiretinal and subretinal implantation of the polyimide electrode array can be done safely in rabbit eyes. Polyimide electrode array showed good biocompatibility in the rabbit eyes for 2 years.

Keywords: retina • transplantation