Calculation of corneal temperature and shrinkage during Laser ThermoKeratoplasty (LTK)

摘要

Purpose. The purpose of this study was to develop a model to predict the corne al temperature and shrinkage during laser thermokeratoplasty and other clinical procedures relying on laser-induced thermal shrinkage of collagenous tissue. Methods. The corneal temperature was calculated by solving the bio-heat equation during laser irradiation using a semi-analytical technique. To calculate shrinkage, we assumed that corneal thermal shrinkage is a thermal denaturation process that follows an Arrhenius equation, and that shrinkage resulting from denaturation is proportional to the amount of thermal damage. We calculated shrinkage for pulsed Ho:YAG laser thermokeratoplasty using the clinical treatment algorithm. Results. The thermal model predicts that the corneal temperature reaches values that may be high enough to induce surface vaporization of the epithelium and thermal damage of the endothelium. Shrinkage calculations show that significant shrinkage is produced only after the third laser pulse. Shrinkage is produced mainly during laser pulses and stops shortly after the start of the cooling phase between laser pulses. Conclusions. These calculations demonstrate that thermal shrinkage can be predicted by combining an optical-thermal model and a thermal denaturation model. Accurate quantitative prediction of the shrinkage effect requires a better knowledge of the dynamics of shrinkage and of the optical thermal response of the cornea.