Laser Physics & Photonic Devices Laboratories, UniSA STEM, University of South Australia, Mawson Lakes, SA, 5095, Australia.
Biomed Phys Eng Express. 2021 Dec 22;8(1). doi: 10.1088/2057-1976/ac3f51.
A realistic model of human retinal tissues to simulate thermal performance of optical laser photocoagulation therapy is presented. The key criteria to validate the treatment effectiveness is to ensure the photocoagulation temperature between 60 and 70 °C is reached in the treatment region of interest. The model presented consists of truncated volumes of the retinal pigment epithelium (RPE) and adjacent retinal tissues. Two cases of choroid pigmentation are modelled to signify extreme cases of human eye difference: albino and dark colour choroid pigmentation. Conditions for consistent heating over the irradiated treatment spot is modelled for laser beams with different intensity profiles: 'top-hat', Gaussian and 'donut' modes. The simulation considers both uniform heating within retinal tissue layers and spatial intensity decay due to absorption along the direction of laser propagation. For a 500m spot, pulse length 100 ms and incident power to the cornea of 200 mW, realistic spatial variation in heating results in peak temperatures increasing within the RPE and shifting towards the choroid in the case of choroidal pigmentation. Finite element analysis methodology, where heat transfer theory governs the temperature evolution throughout tissues peripheral to the irradiated RPE is used to determine the zone of therapeutic benefit. While a TEMdonut mode beam produces lower peak temperatures in the RPE for a given incident laser power, it reduces the volume of retinal tissue reaching excessive temperatures and maximises the zone of therapeutic benefit. Described are simulation limitations, boundary conditions, grid size and mesh growth factor required for realistic simulation.
提出了一种真实的人视网膜组织模型，用于模拟光学激光光凝治疗的热性能。验证治疗效果的关键标准是确保在感兴趣的治疗区域达到 60 至 70°C 的光凝温度。所提出的模型由视网膜色素上皮（RPE）和相邻视网膜组织的截断体积组成。模拟了两种脉络膜色素沉着情况，以表示人眼差异的极端情况：白化病和深色脉络膜色素沉着。对于不同强度分布的激光束，模拟了在照射治疗点上实现一致加热的条件：“平顶”、高斯和“环”模式。该模拟考虑了视网膜组织层内的均匀加热以及由于沿激光传播方向的吸收而导致的空间强度衰减。对于 500m 光斑、100ms 脉冲长度和 200mW 入射角膜功率，加热的实际空间变化导致 RPE 内的峰值温度升高，并在脉络膜色素沉着的情况下向脉络膜转移。有限元分析方法，其中传热理论控制着 RPE 周围组织的温度演变，用于确定治疗受益区。虽然 TEMdonut 模式光束在给定的入射激光功率下在 RPE 中产生较低的峰值温度，但它减少了达到过高温度的视网膜组织体积，并最大限度地扩大了治疗受益区。描述了模拟的局限性、边界条件、网格尺寸和网格增长因子，以实现实际模拟。
