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Lan Yue, Jessy Dana Dorn, Uday Patel, Hassan A Aziz, Lisa C Olmos, James D Weiland, Mark S Humayun; Visual function restored by Argus I and Argus II in the same subject. Invest. Ophthalmol. Vis. Sci. 2016;57(12):No Pagination Specified.
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© ARVO (1962-2015); The Authors (2016-present)
The Argus I (Second Sight Medical Products) retinal implant, containing an array of 16 electrodes, is the first-generation epiretinal prosthesis approved for investigational clinical trials by the US FDA. The second-generation Argus II implant containing 60 electrodes has received market approval in Europe and in the US. Both devices restored some vision to patients blinded for decades by retinitis pigmentosa (RP), yet it remained unclear how the increased number of electrodes affects the visual percepts. Recently, a subject previously implanted with Argus I in one eye received surgical implantation of Argus II in the fellow eye, offering a unique opportunity to study the visual responses of the same subject to both devices.
The subject, who had no light perception in the right eye and bare light perception in the left eye due to advanced RP, was surgically implanted with Argus I in the right eye in 2004, followed by periodic tests of the implant performance for a decade. In 2015, the subject received Argus II in the left eye and has since been regularly followed up. The subject’s visual function was assessed by computer-based tests with high-contrast stimuli, static or moving, presented on a touch screen. Standardized assessments including square localization (SL), direction of motion (DOM) and grating visual acuity (GVA) were all conducted under monocular stimulation.
Electrically elicited phosphenes were present 10 years after implantation of Argus I. Mean error in SL performance was 198 pixels with Argus I ON vs. 470 with the implant OFF. Subject’s performance in DOM, however, was not significantly better with Argus I stimulation and the GVA remained below chart (worse than logMAR2.9). Visual function evaluation 3 months after the Argus II implantation showed improvements in all three tests. With Argus II ON vs. OFF, mean error of SL was reduced from 448 to 140 pixels and the DOM performance was significantly improved (p<<0.05). Further, the subject was able to achieve a GVA of logMAR 2.2±0.2.
This is the first study showing the differential visual responses of the same subject to electrical stimulation from two generations of the Argus prostheses. Our data, albeit preliminary, suggest that Argus II exhibits potential to restore vision of superior spatial resolution. Changes of the Argus II-restored visual function over time will be monitored in future studies.
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.
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