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SF Meyburg, R Eckmiller, M Dapper; In Vitro Study Of Trans-Scleral Wireless Communication For Retina Implants . Invest. Ophthalmol. Vis. Sci. 2002;43(13):4460.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: To explore functional and structural parameters of inductive trans-scleral signal transfer in eye cup preparations for application in retinal prostheses. Methods: Pairs of micro-coils were incorporated in appropriate electronic circuits to serve as primary (transmitting) and secondary (receiving) coils for a wireless, highly localized communication channel. A signal generator for sinusoids in the MHz range was employed together with a digital storage scope for stimulation- and recording purposes. The primary coil was positioned by micromanipulation in 3D during measurements in the air, in liquids, or adjacent to the orbital side of a selected scleral position of an eye cup. The secondary coil was also positioned by micromanipulation and could for example be located adjacent to the corresponding vitreal retinal position of the selected eye wall sector. Eye cups were primarily prepared from young chicken in these in vitro studies and later compared with mammalian eye preparations. Results: Initial measurements with sinusoids at about 10 MHz were performed to compare the transfer gain G(output amplitude / input amplitude) for different coil environments, including: air, buffered physiological solution, and additional insertion of the eye wall of an eye cup preparation at varying coil distances. For an air environment at a coil distance of 2 mm, G was in the range of about 0.5. Defining this gain: G=0.5 as standard of 100%, immersion of this coil arrangement in destilled water yielded a gain reduction to about 50%, whereas immersion in physiological solution caused a gain reduction to only about 90%. Additional insertion of an eye cup between the coils during immersion in physiological solution yielded only a very small further gain reduction to about 85%. Once the solution level was reduced to bring coils and eye cup into the air, the gain reduction increased down to about 40%, but rose up again to 85% with re-immersion. Stable trans-scleral signal transfer at acceptable noise levels was found for input amplitudes at least down to 100 mV. Trans-scleral transfer gain expectedly depended on various parameters such as type of eye, coil properties, signal frequency, orientation of both coils relative to each other and to the scleral surface. The energy absorption of the eye tissue will be discussed. Conclusions: Trans-scleral signal- and / or energy transfer by means of coil pairs is a technologically feasible and physiologically tolerable option of wireless communication with prostheses inside the vitreal cavity including epiretinal retina implants.
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