Surgical feasibility and biocompatibility of the OptoEpiret retinal stimulator

Purpose: Degenerative retinal diseases, i.e. retinitis pigmentosa, cause a severe decline of the visual function up to blindness. To this day treating these diseases remains difficult. One way of conquering the eminent loss of vision is implanting retinal prostheses. In this study we investigated the surgical feasibility and biocompatibility of the newly developed OptoEpiret retinal stimulator. Methods: The OptoEpiret retinal stimulator combines aspects of former projects of our group (epiretinal stimulation [EpiRet3], large stimulating array [VLARS]) and extends the functional range by adding an integrated circuit (IC) based optical capturing system. This solution allows capturing of visual information, visual processing, computing of a stimulus pattern and stimulating the ganglion cell layer all on the implanted 9mm array. In order to investigate the surgical feasibility and biocompatibility our group firstly established an implantation surgery by implanting the OptoEpiret in two cadaveric rabbit eyes. Afterwards the implantation method was transferred into an in-vivo model by implanting inactive arrays in 6 rabbits. In an 8 week follow-up, the rabbits were tested clinically and received funduscopic imaging and OCT-imaging, if possible. After concluding the follow up, histological examination, as well as resin-embedding and thin-slicing of the eyes was performed. Results: The implantation surgery conducted in the cadaveric eyes included phacoemulsification, vitrectomy and insertion of the OptoEpiret array through a 5mm corneal incision. The array was fixated on the retinal pole with a central retinal tack. The procedure was deemed safe and transferred to the in-vivo setting. As main adverse effects, we encountered vitreal hemorrhage, retinal tearing or detachment and difficulties of retinal fixation of the large array. In the follow up, transitional corneal edema caused difficulties in post-surgical imaging. In histological examination gliosis around the area of retinal fixation and mild signs of inflammation were detected. Conclusions: Findings in the implantation surgery lead to the assumption that the OptoEpiret retinal stimulator's implantation surgery is safe and feasible. The follow-up examinations showed good biocompatibility. In further experiments, the functional capabilities will be examined by implanting active devices in an acute setting.