Microelectronics Design for an Implantable High Density Retinal Prosthesis

Abstract

Abstract: : Purpose: The goal of this work is to develop microelectronics for an implantable epiretinal prosthesis using electrical stimulation of the retina for restoring lost vision in patients with Retinitis Pigmentosa and Age related Macular Degeneration. The three major components of the microelectronics are wireless power telemetry, wireless data telemetry and microstimulator. Methods: The implant electronics need power for operation. A wireless power telemetry has been developed that can transmit power using a pair of air coupled coils. The power telemetry operates in a closed loop mode, thereby delivering the ‘just needed’ power. This increases the power efficiency compared to open loop mode and also reduces power dissipation in the implant. The wireless data telemetry for transmitting the stimulus data to the microstimulator uses another pair of coils. This unconventional method results in a hybrid dual–band approach allowing the power and data telemetry to be optimized independently. The microstimulator delivers biphasic current pulses to the retinal tissue. Since different regions of the retina have different stimulation thresholds, the microstimulator is designed to be programmable for different stimulation currents without reduction in resolution. For tissue safety, charge cancellation mechanism periodically discharges the stimulation sites. Results: The power telemetry has been implemented in the form of two IC chips and a coil pair and the closed loop system demonstrated for different loading conditions and coil movements to deliver a maximum of 100 milliwatts. The data telemetry has been implemented with discrete components and a coil pair resulting in data rates up to 2 Mbps. The microstimulator has been implemented as an IC chip for delivering a maximum of 600 microamperes current pulses. Conclusions: An optimal design of the telemetry and microstimulator is important for increasing the lifetime of the batter and efficiency of the electrical stimulus. As we are moving towards a high density prosthesis (1000 electrodes) microelectronics design has a significant impact on the miniaturization and integration of the prosthetic device

Keywords: retina • retinitis • image processing