Numerical simulation of ophthalmic laser surgeries by a local thermal non-equilibrium two-temperature model

Purpose: This paper aims to understand the laser–tissue interaction mechanism during ophthalmic laser surgeries through numerical analysis. The influence of laser parameters and the multipulse technique were investigated. Design/methodology/approach: The ocular fundus was simplified as a multilayered homogenous medium model. Afterward, the multilayer Monte Carlo method was used to simulate the propagation and energy deposition of laser light, and a local thermal non-equilibrium two-temperature model was established to simulate the temperature variation of chromophores and surrounding tissue with different laser wavelength. Findings: Through the model, the selective heating of chromophore (melanin and blood vessels) was clearly illustrated: 1) neglecting the laser energy absorbance by blood in the traditional model will cause significant errors in temperature calculation; 2) the non-thermal equilibrium heat transfer model was needed to obtain an accurate description of the thermal process when the dimensionless pulse width (tp*) is <10⁵. For 532 nm Argon laser, the optimize tp* is around 10⁵ and the appropriate energy density is 5 J/cm²; 3) multipulse technique makes the energy more concentrated within the melanin, thereby reducing the thermal damage in surrounding tissue, with most appropriate pulse number and duty cycle is 10 and 1/10. Originality/value: Taking the blood absorption into account, the different temperature variations of melanin/vessels and surrounding tissue caused by the selective photo-thermolysis were simulated successfully. By understanding the mechanism of laser therapy, laser parameters and multipulse technique are suggested to improve the clinical results.