On the Thermal Elevation of a 60-Electrode Epiretinal Prosthesis for the Blind

Abstract

In this paper, the thermal elevation in the human body due to the operation of a dual-unit epiretinal prosthesis to restore partial vision to the blind affected by irreversible retinal degeneration is presented. An accurate computational model of a 60-electrode device dissipating 97 mW power, currently under clinical trials is developed and positioned in a 0.25 mm resolution, heterogeneous model of the human head to resemble actual conditions of operation of the prosthesis. A novel simple finite difference scheme combining the explicit and the alternating-direction implicit (ADI) method has been developed and validated with existing methods. Simulation speed improvement up to 11 times was obtained for the the head model considered in this work with very good accuracy. Using this method, solutions of the bioheat equation were obtained for different placements of the implant. Comparison with in-vivo experimental measurements showed good agreement.

Retinal safety of near-infrared lasers in cataract surgery

“…The basic geometry for the rabbit eye is taken from a chapter by Gwon,16 while the retinal and choroidal layers are taken from the in vivo rabbit model by Sramek et al 9 The thermal properties of the tissue layers were derived based on the reported water content of each layer, [17][18][19] assuming that the heat capacity and thermal conductivity would be the scaled average of the properties of water and hydrated proteins 20,21 which make up the remainder of the material. The density of tissue was assumed to be that of pure water or fat 22 at 37°C. The optical absorption coefficients for the retinal and choroidal layers were taken from the 1064 nm data in Hammer et al 23 Since protein has negligible absorption in the near-IR, the remaining ocular layers were assumed to have absorption coefficients proportional to the water content.…”

“…In this model, we derived them for each tissue layer from reported water content, which made them somewhat different from those in previously reported models. 22,33,34 A careful measurement of these properties is likely to improve temperature calculations slightly, but the greatest source of uncertainty is the absorption coefficients. These are not as easily defined and vary by position in the eye, from subject to subject and from species to species.…”

Contactless Liquid Sensing Technique Using a Quartz Oscillator

“…(50) In terms of neural stimulators, stimulation safety is related to two main factors: power dissipation at tissue and by implanted electronics, and charge balancing (zero net remaining charge after biphasic current stimulation). A rise in temperature of 1-2 ℃ above the normal body temperature could lead to tissue damage; (51) therefore, the total power dissipation of the implanted stimulator should be less than tens of mW to prevent an excessive rise in temperature. Maintaining charge balance during electrical stimulation is also important.…”

Design and analysis of energy recyclable bidirectional converter with digital controller for multichannel microstimulators

“…• C [5] with high stimulation Paul Jung-Ho Lee and Amine Bermak are with the Smart Sensory Integrated Systems (S2IS) Lab, the Department of Electrical and Computer Engineering, Hong Kong University of Science and Technology, Clear Water Bay, Hong Kong, China (e-mail: jhleeaa@ust.hk, eebermak@ust.hk).…”