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T. Laube, H. Akguel, T. Schanze, M. Goertz, I. Bolle, C. Brockmann, N. Bornfeld, EPI–Ret Group; First Time Successful Epiretinal Stimulation with Active Wireless Retinal Implants in Göttinger Minipigs . Invest. Ophthalmol. Vis. Sci. 2004;45(13):4188.
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Purpose: The function of retinal implants needs to be tested in an animal model, which provides a close surgical relationship to human eyes and which allows function tests of the visual prosthesis by the registration of cortical evoked potentials. For this we started implantation and testing of active wireless retinal implants in minipigs. Methods: We implanted telemetrically controlled 24–channel epiretinal implants in 3 minipigs. After the removal of the lens we performed a complete vitrectomy. The electronic part of the implant, embedded in a silicone based intraocular lens, was fixed by transscleral sutures. The implant’s platinum polyimide electrode array was fixed by a retinal tack on the central part of the retina. We tested implants function by recording artifacts with ERG electrodes and three silver–silverchloride electrodes implanted epidurally above primary visual cortex of one hemisphere. Recording electrodes’ function was checked by recording visually evoked potentials. For implants activation we positioned the coil of the external transceiver in front of the implanted eye. We proved successful retinal stimulation by recording of electrically evoked cortical responses and threshold estimations for different stimulation currents and waveforms. Results: We measured stimulation artifacts with eye and cortex electrodes, indicating implants function. Reprogramming of the implants stimulation wave forms resulted in related changes of the artifacts. We found first cortical responses about 20 ms post stimulation, which was in correspondence with previous findings obtained with non–wireless implants. Thresholds varied with respect to the estimated distance between stimulation electrode and retina. However, we found that stimulations thresholds of much less than 100 µA can be achieved in cases with excellent contact between stimulation electrode and retina. Conclusions:We have demonstrated the first successful stimulation with a wireless epietinal implant in minipigs. This is an important proof of principle as required for the development of retinal implants for humans.
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