Purchase this article with an account.
J. Sandeau, G. Caillibotte, R. Jacobs, J. Kandulla, R. Brinkmann, R. Birngruber, G. Apiou–Sbirlea; Mathematical Modelling of Conductive and Convective Heat Transfers and Temperature Simulations in Retinal Laser Applications . Invest. Ophthalmol. Vis. Sci. 2006;47(13):5719.
Download citation file:
© ARVO (1962-2015); The Authors (2016-present)
Ophthalmic laser applications such as tumor thermo treatment, transpupillary thermotherapy or photodynamic therapy deal with long term and large laser spot exposures. Under these conditions convective heat transfers in the choroid must be considered in addition to the usually calculated heat conduction. A numerical model which takes global conduction and local choroidal perfusion into account was developed and applied to various clinically realistic laser exposure situations in order to quantify the influence of choroidal blood flow in thermal laser applications at the fundus of the eye.
Heat conduction is modelled in a homogeneous and isotopic material using water thermal constants. Forced heat convection due to the choroidal blood flow is calculated assuming a constant heat perfusion in the choroid. As the geometry and the optical parameters of the layers are individually different, we developed a procedure which allows to specifically take the geographical and optical conditions of the absorbing structures at the fundus into account. Finally we developed subroutines for each light absorbing layer in order to define heat generation and heat dissipation terms based on a numerical finite volume and element method. In order to calibrate the numerical modelling results, the calculated temperature profiles were compared with results from an analytical model which takes convection into account by a uniform and global perfusion term. Moreover preliminary experimental in–vivo temperature measurements using a novel non–contact method served as validation of the modelling results.
The numerical and analytical calculations assuming global convection were almost perfectly in agreement. Local convection comparing calculated results with experimental in–vivo measurements in rabbits resulted in perfusion rates between 0,3 and 4 s–1 depending on the assumed thickness of the choroidal perfusion layer necessary for modelling convective temperature reductions of 33 %.
We have developed a thermal model which for the first time allows to realistically model local convection due to choroidal blood flow. Preliminary results indicate a substantial influence of choroidal heat convection in retinal thermotherapy if long exposures and large spot sizes are used. If realistic optical and thermal datas are available, precise temperature profiles can be calculated in order to optimize thermal laser applications in the eye.
This PDF is available to Subscribers Only