The Architecture, Design, and Electromagnetic and Thermal Modeling of a Retinal Prosthesis to Benefit the Visually Impaired

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Title: The Architecture, Design, and Electromagnetic and Thermal Modeling of a Retinal Prosthesis to Benefit the Visually Impaired
Author: DeMarco, Stephen Christopher
Advisors: Wesley Snyder, Committee Member
Griff Bilbro, Committee Member
Gianluca Lazzi, Committee Co-Chair
Wentai Liu, Committee Co-Chair
Abstract: This dissertation describes the design and study of a retinal prosthesis for individuals who have suffered loss of vision from degeneration of the outer retina. Retinitis pigmentosa and age-related macular degeneration lead to blindness through progressive loss of retinal photoreceptors. Experiments reveal that direct electrical stimulation of remaining ganglion cells in degenerate retina elicits visual percepts in blind RP/AMD patients. This motivates research toward the development of a retinal prosthesis system involving an implantable stimulator microchip to compensate the defective photoreceptors. Many prostheses do not reside fully inside the body, but consist of an implantable stimulation unit and an external unit. This underscores a need in the retinal prosthesis to deliver power and support high-speed bi-directional communication with the implant wirelessly. The current progress in the types of non-invasive connections to bio-implants is reviewed as it relates to the power and communication needs of prostheses. The extraocular unit is a hardware-reconfigurable system based on FPGA technology which produces real-time instructions for the implantable micro-stimulator IC. The current retinal stimulator IC is designed to provide electrical stimulation to the remaining ganglion cells of post-degenerative retina. Also described is a design technique to significantly reduce the on-chip area of the stimulus circuits. This yields more output channels per chip area, thereby raising the stimulation resolution. Temperature elevation in the eye and head tissues associated with the retinal prosthesis is studied. A high resolution 2D human head and eye model is developed at 0.25mm spatial resolution with associated dielectric and thermal properties suitable for numerical simulations. The Finite Difference Time domain method (FDTD) with material independent absorbing boundary conditions is used to predict the specific absorption rate (SAR) induced from electromagnetic exposure to wireless inductive telemetry with the implant. A detailed heating pattern in the eye tissues due to the SAR and power dissipation in the implanted stimulator is computed using a time-domain numerical implementation of the bioheat equation.
Date: 2003-05-19
Degree: PhD
Discipline: Computer Engineering

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