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Eberhart Zrenner, Karl-Ulrich Bartz-Schmidt, Florian Gekeler, Udo Greppmaier, Stephanie Hipp, Gernot Hoertdoerfer, Christoph Kernstock, Akos Kusnyerik, Helmut Sachs, Katarina Stingl; Seeing With Subretinal Electronic Implants: Study in Ten Patients With Wireless Implant Alpha-IMS. Invest. Ophthalmol. Vis. Sci. 2012;53(14):6948.
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Subretinal microphotodiode arrays with 1.500 pixels are able to restore vision up to reading capability (Zrenner et al . Proc. R. Soc. B 2011, 278: 1489ff). Here we report about the first phase of a multicenter trial with the wireless implant Alpha-IMS (Retina Implant AG, Tübingen, Germany).
Each of the 1500 subfoveal photodiodes within a 11 by 11 deg field controls an amplifier that, depending on the strength of the light, ejects currents onto bipolar cells via an electrode (Stett et al 1999). Power and control signals are supplied by inductivity via a subdermal retroauricular coil from which a subdermal cable leads to the eyeball. Ten patients have received the new implant since 2010 (average age 45.95±7.9; 5 males, 5 females). Function was tested by four procedures: 1. Monitor-based standardized tests with controlled conditions for testing light perception threshold, light localization and movement (Wilke et al. 2007), as well as grating acuity and Landolt C-rings (2 or 4 AFC); 2. Recognition tasks at a table setting with tableware and geometric objects; 3. Reading of letters; 4. Outdoor activity, observed either by staff members or reported by the patients. All tests were also conducted with the device swiched off as control.
In all ten patients the chip was at the desired subfoveal position except in two patients where it was slightly parafoveal. Proper chip function was proven by measuring chip output via electroretinography. All patients were able to perform the function tests except one where a loss of inner retina function was observed after surgery. Results in all other patients were: light perception: 9/9, light localization: 8/9; motion recognition 5/9; grating resolution 8/9 (up to 3,3 cycles/degree); Landolt C rings 2/9 (up to VA= 0,036); recognition of geometric objects 8/9; recognition of objects in table setup 8/9; Letter reading 4/9; clock hands reading 3/9; grey scale differentiation 6/9; improved outdoor mobility and activity 5/9. Patients reported numerous beneficial visual experiences in daily life with regained recognition of unknown objects, recognition of facial or clothes’ characteristics, moving objects in nature and traffic, improved self-sustaining actions (recognition of doors, door handles), recognition of small objects (glasses, telephone, stapler, washing basin, even dice and numbers of dots on dice), improved mobility.
Careful psychophysical testing and patient daily-life reports show that the wireless Alpha-IMS implant restores useful visual abilities in blind RP-patients. Subretinal surgery for positioning chips subfoveally is safe and the multicenter part of the study has been started.
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