Bio-Heat Transfer Model of Human Eye Subjected to Retinal Laser Irradiation

Retinopathy is a surgical process in which maladies of the human eye are treated by laser irradiation. A two-dimensional numerical model of the human eye geometry has been developed to investigate steady and transient thermal effects due to laser radiation. In particular, the influence of choroidal pigmentations and choroidal blood convection — parameterized as a function of choroidal blood perfusion are investigated in detail. The Pennes bio-heat transfer equation is invoked as the governing equation and a finite volume formulation is employed in the numerical method. The numerical model is validated with available experimental and two-dimensional numerical results. For a 500 μm diameter spot size, laser power of 0.2 W, with 100% absorption of laser radiation in the Retinal Pigmented Epithelium (RPE) region, the peak RPE temperature is observed to be 175 °C at steady state, with no blood perfusion in choroid. It reduces to 168.5 °C when the choroidal blood perfusion rate is increased to 23.3 kgm⁻³s⁻¹. However, under transient simulations, the peak RPE temperature is observed to remain constant at 104 °C after 100 ms of the laser surgery period. A truncated three-dimensional model incorporating multiple laser irradiation spots is also developed to observe the spatial effect of choroidal blood perfusion. For a circular array of seven uniformly distributed spots of identical diameter and laser power of 0.2 W, steady and transient temperature evolution are presented with analysis.