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I. Krisch, M. Görtz, B. Hosticka, EPIRET 3 Group; A Wireless Epiretinal Prosthesis:The Technical Features - Communication, Power Management and Signal Processing. Invest. Ophthalmol. Vis. Sci. 2008;49(13):3026.
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This epiretinal prosthesis bypasses neural defects and then enables direct electrical stimulation of nerve cells. In this contribution, we focus on the electronic part of the implant system and discuss topics like system design, data and power transfer, and coding the signals. Typically, in conventional implants, this transfer is supported by a cable connection. Our system is based upon an implantable micro electro stimulator which is powered and addressed wireless via an inductive link.
The hardware used in the clinical trial consists of an extraocular and an intraocular part. The extraocular part includes a conventional computer system, a transmitter unit and a transmitter coil attached to a special holder similar to an eyeglass frame. The software on the computer transforms scientific patterns into interpretable stimulation pulse sequences for the stimulation electrodes. Stimulation data and control signals are sent to the transmitter unit feeding the externally connected antenna coil.Technically, the intraocular part is a remotely controlled fully intraocular wireless retinal prosthesis mainly consisting of a receiver and a stimulator module. The receiver coil inside the eye acquires the electromagnetic signals and passes them onto the microchip which operates as a receiver. The CMOS receiver carries out all tasks necessary for power and data recovery. The extracted signals are forwarded to the stimulator chip. The CMOS stimulator generates the adaptable stimulation pulses and activates the selected electrodes.
Significant miniaturization of the implant components enables new surgery techniques. The entire system is proven functioning in a clinical trial. The inductive link is able to bridge a gap of 25 mm in order to power the intraocular part of the implant system. Data transmission is stable, i.e. the wireless transmission channel tolerates any eye movements and nods. A data rate up to 200 kbit/s can be obtained. The implant can drive up to 25 stimulation electrodes with charge balanced current pulses for stimulation.
Implantation of the wireless device is safe and the system is suitable to elicit visual sensations in blind RP patients. The system is the first functioning retinal prosthesis which avoids any cable connections crossing the eye’s wall. Major problems in the design and assembly of a prosthesis for artificial vision could be solved in this approach.
Clinical Trial: :
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