A Parametric Investigation of Corneal Laser Surgery Based on the Multilayer Dynamic Photothermal Model.

Corneal laser surgery is a widely used method for the treatment of ocular myopia, hyperopia, and astigmatism. Although it is a well-established technique, the photothermal properties of the cornea are often overlooked, causing unexpected changes in temperature during laser irradiation. Therefore, there is a need for further investigation of the temperature response of the cornea under laser irradiation. In the present work, a photothermal corneal numerical model is presented, assuming the stratification of the cornea with laser ablation in an uncoagulated layer, a coagulated layer, a dehydrating layer, a dried layer, and a carbonized layer. The modified Pennes' bioheat transfer equation and Lambert-Beer's law are applied to simulate heat transfer in the corneal tissue during laser irradiation. And the corneal dynamic photothermal parameters are considered in the proposed model. The central surface temperature, the boundary and thickness of each layer, and the thermal damage during laser irradiation are investigated. From the model, it was found that in the steady-state process, the thickness of the coagulated layer was 2.6, 14.4, and 52.4 times larger than that of the dehydrating layer, the dried layer, and the carbonized layer, respectively. The thickness of the corneal thermal damage gradually increased, and reached a peak of 0.196 mm at about 18.2 ms. Subsequently, it sharply decreased by 0.01 mm before stabilizing. On this basis, the influence of laser intensity is investigated. The parametric investigation and analysis presented provide a theoretical basis for corneal laser surgery, which can be used to improve our understanding of laser-tissue surgery.