Heating of the Eye by a Retinal Prosthesis: Modeling, Cadaver and In Vivo Study

In order to develop retinal implants with a large number of electrodes, it is necessary to ensure that they do not cause damage to the neural tissue by the heat that the electrical circuits generate. Knowledge of the amount of power that induces thermal damage will assist in development of power budgets for implants, which has a significant effect upon the design of the prostheses circuitry. In this study, temperatures were measured at multiple locations on the retina while the retina was heated in cadaver and in vivo preparations using a variety of prosthesis implantation sites. A finite element thermal model of the cat eye was also created and validated by the cadaver and in vivo tests, allowing for a much larger spectrum of thermal influences to be evaluated without additional animal experimentation. To ensure that retinal tissue temperatures are not increased by more than 2 degrees C, a 5 mm x 5 mm, suprachoroidally implanted heating element must not dissipate more than 135 mW (5.4 mW/mm(2)).