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A. Fernandes, G.M. L. L. Silva, D.K. E. Carvalho, P.R. M. Lyra, R.C. F. Lima; The Use Of An Axisymmetric Formulation Of The Finite Volume Method For The Thermal Analysis Of The Retina And Other Ocular Tissues Following Implantation Of Retinal Prosthesis . Invest. Ophthalmol. Vis. Sci. 2006;47(13):3174.
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© ARVO (1962-2015); The Authors (2016-present)
To calculate the temperatures profiles and the thermal damage function in the retina and other tissues of human eyes implanted with an epiretinal or a subretinal prostheses designed to partially restore vision.
The temperatures profiles and the thermal damage function were calculated by using an unstructured Finite Volume Method (FVM) that was developed for axisymmetric models. This formulation used a vertex–centered FVM with an edge–based data structure. The Bioheat Transfer Equation was used to guide the physical process. In order to discretize two–dimensional arbitrary domains, we used a computational system which generated triangular meshes. The adopted mesh generator provided the mesh data in an element–based data structure. The implementation of the finite volume solver required a pre–processing stage in order to convert the element–based data structure into an edge–based one. The edge–based data structure and the physical properties were then fed into a FVM computational solver. We obtained the natural basal temperature distribution in the absence of any external heat sources. The external environment temperature used was 20°C. The thermal analysis was then performed for the epi and subretinal silicon implants. The subretinal implant measured 3mm of diameter, 70µm thickness, and the dissipated electrical power was 2.5 µW. The epiretinal implant measured 4.6mm x 4.7 mm, 30µm thickness, and the dissipated electrical power was 46 mW.
For the subretinal implant the highest temperature was obtained at the chip–outer retinal interface (36.8 °C). The steady–state condition was reached after 70 s. The thermal damage (Ω) reached the value of 0.53 after 100 days when denaturation started. It was complete (Ω=1) after 190 days. In the case of the epiretinal implant, which dissipated greater electrical power, the temperature reached 36.84 °C at the implant–retinal interface; steady–state after 37s; Ω=1 after 193 days.
The computational model we developed has shown to be an useful tool to determine the temperatures and heat damage in several ocular tissues following the implantation of retinal prostheses.
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