Long Term Retinal Function after Repeated Ab Externo Implantation and Explantation of Subretinal Electronic Devices in Rabbit

Abstract

Abstract: : Purpose: To ensure safe multiple exchange of subretinal prostheses without serious effects on global retinal function as to be evaluated by functional and morphological parameters. Methods: Polyimide foil strips (42 x 2 x 0.05mm) carrying 32 Titanium-nitride electrodes (30 electrodes of approximately 1.96 x 10-3 mm2 each and 2 of approximately 1.9 mm2 each) were implanted into the subretinal space for electrical stimulation in rabbit eyes (n=2) using a novel ab externo subretinal implantation and explantation technique (ARVO, 1998, no.4161, 2002, no.4471). During a period of 10 months foil strips were implanted 4 times and explanted 3 times in the right eye of rabbit 1 with intervals of 8 weeks (Implant 1), 6 weeks (Implant 2), and 26 weeks (Implant 3), using always the same ab externo access into the subretinal space. In rabbit 2, which had undergone its first implantation 13 months ago, the stimulation foil was implanted adjacent to the already present first device. Electroretinograms (ERGs) and visual and electrically evoked cortical potentials (VEPs and EECPs) were recorded immediately after the final implantation. Results: It was possible to perform repeated ab-externo surgery smoothly through the same subretinal implantation channel in the eye of rabbit 1. A second surgery was successfully performed 12 months after the first surgery in rabbit 2. Both ganzfeld ERGs and VEPs showed a regular global retinal response and intact visual pathway function of the implanted eye respectively (rabbits 1 & 2). Subretinal electrical stimulation elicited retinal (rabbits 1 & 2) and cortical responses (rabbit 2). Histology showed in general well preserved retinal pigment epithelium and retinal structures in the implantation channel, but atrophic alterations of the parvangiotic rabbit retina were evident at the tissue above and below the implant. Conclusions: Global retinal function is well preserved after multiple exchanges of subretinal devices, although degenerative changes at the tissue above and below the implants were observed. This surgical technique might enable an optional explantation and implantation of a subretinal device into an intact retinal region even several months after the first implantation in rabbits.

Keywords: retina • vitreoretinal surgery • electrophysiology: non-clinical