Author: Stanislao Rizzo
Development of a long-term ocular tissue biocompatible fixation mechanism and surgical technique for an autonomous epiretinal prosthetic device, the NR600 Implant, with an intraretinal electrode array to restore visual function in patients with severe to profound visual impairment due to inherited retinal degenerative diseases.
Nano-Retina has developed a unique anchoring system made of an elastic metal helical coil, in which the epiretinal prosthetic device interfaces the retina exclusively, while the anchoring parts are secured in the ciliary sulcus similar to IOL haptics, thus minimizing retinal contact, ensuring controlled forces and long-term position stability. The NR600 implant system is delivered into the eye in a folded state via a limbal incision using a tissue and electrodes protective tool. Once the system is secured in the anterior segment, the helical structure holding the implant is released inside the eye and guided securely by the surgeon to its designated retinal site in the macular region without applying any direct forces on the retina by the surgeon.
The system has been extensively tested in the porcine model with long-term follow-up prior to commencing an interventional multicenter clinical study in retinitis pigmentosa patients with vision of light perception and worse. Baseline examinations were performed before implantation and patients were evaluated at 1-2 days post-op and periodically thereafter.
Eight patients were implanted to date with an average of 10.6 ± 8.6 months (range 1.5 – 22 months) of follow-up, and all tolerated the procedure well, demonstrating good and fast recovery. Four (4) subjects were implanted in the right eye and 4 in their left eye (average axial length is 23.4±0.9mm). Three (3) patients were phakic, 5 aphakic, and 1 pseudophakic prior to implantation. The implantation surgery lasted an average of 02:49 hh:mm (range 2:19 – 3:25). Surgical-related adverse events included mild corneal edema and mild episcleritis, which were transient and resolved with medications. All the implants were functional when tested after the surgery, and phosphene perception has been demonstrated in all patients. In one case the implant was unintentionally positioned away from the fovea, resulting in poor localization of the IR beam by the implant. All implants remained at the implantation site, the fundus remained clear with no evidence of fibrotic reaction, and the implant surface as well as the fixation parts stayed free of tissue debris. OCT images showed no thinning or morphological changes to the retina in the vicinity of the implant, with only slight tissue elevations immediately adjacent to the implant in some cases.
Patients who had bare or no light perception prior to the implantation, regain visual capabilities that may significantly improve their quality of life. Implantations in humans corroborate the good safety outcome of the preclinical study. The advantages of this surgical approach are that it builds on familiar procedures of IOL fixation and that the majority of the surgery focuses on the anterior segment, away from the retina. The results of the study establish safety of the NR600 prosthesis and positive efficacy for otherwise blind patients.