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U. Thelen, H. Gerding; The Minimal Invasive Retinal Implant (miRI) Project: Experimental Testing of Electrodes Completely Penetrating the Sclera, Choroid, and Retina in Rabbits . Invest. Ophthalmol. Vis. Sci. 2006;47(13):3194.
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To investigate the feasibility of a minimal invasive retinal implant (miRI) that consists of a nearly complete extraocular device with the only exception of stimulating electrodes that contact the retina by direct scleral and choroidal penetration.
Surgical technique: Single or multiple metallic electrodes (diameter: 90 to 400 µm) were implanted in 9 rabbits after enzyme (plasmin) assisted vitrectomy so that the sclera, choroid, and retina were completely pentrated. The site of implantation had either been treated by cryocoagulation previously or was untreated (n= 5). Follow–up results were documented during a postoperative period of up to 10 months including standardized regular clinical visits, digital anterior and posterior segment imaging, and electroretinography. Histological analysis was performed by serial sections, standard staining and immunehistochemistry.
Completely penetrating electrodes could be implanted without complications in 7 of 9 animals. In two cases the retina detached due to intraoperative complications not related to the insertion of electrodes. Choroidal haemorrhage was always limited without further complications. In small diameter implants hardly any visible choroidal haemorrhage occurred. Secondary epi–, sub–, and intraretinal proliferations were regionally limited to the area of implantation and were related to the dimension of implants. Large diameter implants (>200 µm) caused a regional proliferation whereas in eyes with small diameter electrodes there was hardly any proliferative reaction detectable funduscopically. No significant electroretinographic changes (b–wave amplitude and implicite time) occurred during follow–up. Histologically the retina around large diameter electrodes presented a regional fibroglial transformation. The retina around small diameter implants showed only minor changes
Results of this preliminary study demonstrate that penetrating electrodes can be placed at the posterior segment of the eye without complications. The use of small diameter electrodes leaves the penetrated intraocular structures mainly intact. Data presented here clearly demonstrate the feasibility of an extraocular retina implant with penetrating posterior segment stimulation electrodes.
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