Thermal elevation in the human eye and head due to the operation of a retinal prosthesis

An explicit finite-difference time-domain formulation of the bio-heat equation is employed with a three-dimensional head eye model to evaluate the temperature increase in the eye and surrounding head tissues due to the operation of the implanted stimulator IC chip of a retinal prosthesis designed to restore partial vision to the blind. As a first step, a validation of the thermal model and method used is carried out by comparison with in vivo measurements of intraocular heating performed in the eyes of dogs. Induced temperature increase in the eye and surrounding tissues is then estimated for several different operational conditions of the implanted chip. In the vitreous cavity, temperature elevation of 0.26/spl deg/C is observed after 26 min for a chip dissipating 12.4 mW when positioned in the mid-vitreous cavity while it is 0.16/spl deg/C when the chip is positioned in the anterior portion between the eye's ciliary muscles. Corresponding temperature rises observed on chip are 0.82/spl deg/C for both the positions of the chip. A comprehensive account of temperature elevations in different tissues under different operational conditions is presented.