The Minimal Invasive Retina Implant (miRI) Project: Long-Term Angiographic and Histopathological Findings After Implantation of Devices Carrying Microelectrodes Penetrating the Sclera, Choroid and Retina

Abstract

Purpose:: To develop a minimal invasive retinal prosthesis (miRI) that will be implanted on the outer scleral surface with stimulating microelectrodes penetrating the sclera, choroid, and retina. To analyze angiographic and histopathological findings after implantation of protypes in a long-term experimental series.

Methods:: Minimal invasive retina implant prototypes carrying 2-10 penetrating electrodes ( = 27) were implanted in 5 cynomolgus monkeys. 2 implants underwent a forced implantation with immediate penetration of electrodes during surgery. 3 implants were placed so that penetration developed slowly. Follow-up was 3 (n=1) - 6 (n=4) months. Fluoresceine angiography was documented preoperatively, in the 2. postoperative week, after 7-8 weeks, 12-13 (n=5), and 26 weeks (n=4). Angiography was performed according to a standard protocol (1 second intervals until late venous phase, late image after 5-10 minutes). Finally all eyes were processed by serial sectioning in order to analyze each site of electrode penetration.

Results:: 23 of 27 implanted microelectrodes were penetrating the eye with final position of the electrode peak within the retina or vitreous. Two electrodes in eyes with forced implantation were inducing a mild and local pigmentary reaction. All other electrodes did not cause clinically visible reactions. In flurorescence angiography a very limited staining occurred directly around electrodes. Angiographic signs of neovascularization, significant retinal or choroidal vascular changes, or remote effects were not observed. All sites of penetration could be reconstructed histologically. Electrodes with forced penetration (n=4) presented regional retinal destruction (up to 200 µm radius) and in 2/4 cases a regional outer retinal degeneration. 1/23 penetration sites presented a very limited epiretinal proliferation. Intraretinal tissue reactions towards the 19 electrodes with slow penetration was very limited with complete preservation of the retinal structure in the vicinity of penetration.

Conclusions:: Penetrating electrodes are very well tolerated on a long-term scale as could be demonstrated by funduscopic, angiographic and histopathological results. Email: [e-mail]

Keywords: retina • retinal degenerations: hereditary • retinal connections, networks, circuitry