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S. K. Kelly, W. F. Ellersick, P. Doyle, S. F. Cogan, W. A. Drohan, D. B. Shire, J. L. Wyatt, J. F. Rizzo; Electrical System and Circuit Considerations for a Chronic Retinal Prosthesis. Invest. Ophthalmol. Vis. Sci. 2010;51(13):3025. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
This work is related to the efforts of the Boston Retinal Implant Project to develop a sub-retinal prosthesis to restore vision to the blind. Specifically, this poster presents aspects of both system and circuit designs for the prosthesis. This design includes a variety of electrical components and systems, each of which has a number of parameters to be optimized. Design tradeoffs are considered to balance parameter optimizations.
Prosthesis performance, size, power, and safety were accounted for in this design. A bidirectional communication system and power telemetry system were integrated with a conformal, biocompatible secondary coil and an unobtrusive primary coil. The custom integrated circuit design is size-limited to fit in the hermetic case on the eye, but must be low-power, flexible enough to use as a research device, and include a wide variety of safety features.System-level calculations were performed to balance the separate parameter optimizations. Spice simulations were performed to verify the design of the inductively coupled coil system. Spice simulations in Cadence were performed to generate initial area and power estimates. Safety features were tested with more in-depth simulations of potential failure modes.
An electrical system is presented that satisfies the size, power, performance, and safety requirements for this implant. The prosthesis ASIC fits in a 5mm x 5mm pad frame, dissipates less than 10 mW of standby power, and has independent current amplitude and timing, and the ability to use electrodes as current returns. Simulation results are shown for the telemetry system, electrode current drivers, and safety features. Failure modes are explored for the electrode safety monitors and other safety features, and evidence is presented that single points of failure will not cause dangerous situations.
A variety of parameters have been explored for each electrical element of the subretinal prosthesis. Proof-of-concept simulations have been used to verify the design, and the design is ready for implementation and fabrication.
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