Testing of Chronically Implanted 49-Channel Retinal Prosthesis by Suprachoroidal-Transretinal Stimulation (STS) in Patients with Advanced Retinitis Pigmentosa

Abstract

Purpose: We have reported that patients with advanced RP can recognize a large target with an implanted 9 channel STS-type retinal prosthesis (Fujikado, IOVS 2011). We have developed a 49-channel 2^nd -generation STS retinal prosthesis, and animal experiments showed that it can be safely implanted in a scleral pocket (Fujikado, Proc IEEE 2013). We report the results of a clinical trial that evaluated the safety and effectiveness of the 49 channel STS retinal prosthesis.

Methods: Three patients with advanced retinitis pigmentosa (RP, 2 man and 1 woman, ages: 42, 61, 62 years) were studied after an approval of the protocol by the IRB of the Osaka University. To evaluate the safety of the 49 channel STS retinal prosthesis, complications during surgical implantation of the prosthesis, postoperative complications, and the durability of device were investigated. To evaluate the efficacy of the prosthesis, we performed localization tests in which the deviation of the reaching point from the center of a randomly presented white square on the touch-panel was evaluated. The follow-up period was 1 to 9 months.

Results: No complications developed during the implantation surgery in all cases. The electrode array was implanted in the scleral pocket located under the parafoveal inferio-temporal retinal area which was identified by optical coherence tomography in all cases. Postoperative side effects were observed in Patient 2 in which filamentary keratopathy and iridocyclitis were observed 1 and 2 months after the surgery. The complications were successfully treated by eye drops. The implanted devices were functioning during the follow-up period in all cases. The number of electrodes which elicited phosphenes with a current less than 1 mA and without evoking somatosensory sensation was 36, 34, and 18 in Patients 1 to 3 respectively. The results of localization test were significantly better with the device switch ON than with it switched OFF in Patient 3, in whom the electrode array was inserted in the scleral pocket closer to the fovea.

Conclusions: The 49 channel STS-Japan retinal prosthesis can be implanted without major complications and can elicit phosphene in patients with advanced retinal pigmentosa. More effective vision could be obtained in the case in which the electrode array was inserted closer to the fovea.