Department of Engineering Applications of Laser, National Institute of Laser Enhanced Sciences, Cairo University, Giza, 12613, Egypt.
Medical Applications of Laser Dept., National Institute of Laser Enhanced Sciences, Cairo University, Giza, 12613, Egypt.
Phys Eng Sci Med. 2021 Mar;44(1):221-227. doi: 10.1007/s13246-021-00971-x. Epub 2021 Jan 21.
Corneal reshaping using laser ablation effect is a well-known ophthalmologic operation implemented to correct many vision disorders. UV pulsed lasers are utilized in this surgery due to their high absorption in corneal tissue without affecting the other parts of the eye. Ideally ablation may not be associated with heat transport, since high temperature is the enemy of soft tissues. However, the thermal effect of this procedure can cause tissue damage if the temperature rises above the safety level without appropriate handling. In the present study, we try to find the trade-off between efficient ablation and minimal temperature rise. So the thermal effect on the corneal tissue after applying five UV wavelengths; 193, 210, 213, 223 and 248 nm has been simulated and investigated by solving Penne's bio-heat transfer equation using the finite element method. A 3D model of the human cornea is constructed using COMSOL Multiphysics computer software and the temperature rise is determined at the end of the laser pulse. The same spot size and pulse duration are used for each wavelength. While the absorption coefficient of the corneal tissue is the only variable as it is a wavelength dependent. The proposed results show that, the heating effect is directly proportional to the absorption coefficient. The highest recorded temperature was 259 °C at 193 nm, while, the minimum value was (70.1 °C) recorded at 248 nm at which the cornea has the lowest absorption coefficient.
利用激光消融效应重塑角膜是一种众所周知的眼科手术，用于矫正多种视力障碍。由于在角膜组织中具有较高的吸收率，而对眼睛的其他部位没有影响，因此在这种手术中使用了紫外脉冲激光。理想情况下，消融过程不应伴随热传递，因为高温是软组织的敌人。然而，如果在没有适当处理的情况下，温度升高到安全水平以上，该过程的热效应可能会导致组织损伤。在本研究中，我们试图在高效消融和最小温升之间找到折衷方案。因此，通过使用有限元法求解 Penne 生物传热方程，模拟并研究了角膜组织在应用五种紫外波长（193、210、213、223 和 248nm）后的热效应。使用 COMSOL Multiphysics 计算机软件构建了人眼角膜的 3D 模型，并在激光脉冲结束时确定了温升。对于每种波长，使用相同的光斑尺寸和脉冲持续时间。而角膜组织的吸收系数是唯一的变量，因为它是波长相关的。提出的结果表明，加热效果与吸收系数成正比。在 193nm 处记录到的最高温度为 259°C，而在 248nm 处记录到的最低温度为（70.1°C），此时角膜的吸收系数最低。
