Surgical Approach and Initial Histological Results of an Implantable High Resolution Epiretinal Stimulation Array in the Porcine Model

Abstract

Abstract: : Purpose: To describe our initial experience and provide histological correlation of an implantable epiretinal stimulation array in the porcine model. Methods: A high resolution epiretinal stimulation array currently being developed jointly between the Naval Research Laboratory and Georgetown University–Washington Hospital Center was surgically implanted into 5 pig eyes. Initial preparation consisted of a standard 3 port pars plana vitrectomy (ALCON) and lensectomy in which the anterior capsule was left intact. This was followed by the placement of a 5 mm shelved sclersotomy incision placed approximately 3mm posterior to the limbus of the prone subject. A surgical bolster was placed over the 5 mm incision with the array being advanced under it into the vitreous cavity. The bolster was then tightened over the protruding microwire cable. The device was placed onto fovea by direct manipulation of the cable and device using intravitreal (DORC) forceps. Silicone oil was placed into the eye to fix the device in place for one hour. The device was subsequently removed, wounds were closed, and the globe was enucleated and injected with fixative. Contralateral eyes of the same animal served as controls. All eyes were sent to the Armed Forces Institute For Pathology (AFIP) for light and electron microscopic analysis. Results: In total, 5 experimental and 5 control eyes were submitted for pathological analysis to the AFIP. Rigorous light and electron microscopic evaluation revealed normal retina without evidence of toxicity or anatomical alteration when compared to normal controls in all 5 eyes. In particular, there was no evidence of anatomical shearing, destruction of any of the inner or outer retinal layers, direct cellular toxicity or morphologic alteration in the zones where the micro–array was fixed. Conclusions: While challenging, surgical implantation of high resolution epiretinal stimulation arrays in the porcine model in the manner described represents a technically feasible procedure. Notably, this approach results in no detectable microscopic destruction or alteration of the normal retina. The utility of such procedures, especially in light of the growing field of epiretinal stimulation microarrays, remains to be seen. Further research is warranted.

Keywords: macula/fovea • pathology: experimental • retinal connections, networks, circuitry