Investigations on laser thermokeratoplasty

摘要

Abstract: Homogeneous deep intrastromal coagulations are thought to be optical for effective laser thermokeratoplasty. We therefore investigated the thermal effects created by two different flashlamp-pumped IR lasers (Er:glass and Cr:Tm:Ho:YAG) as well as two different application modalities (direct fiber contact and intrastromal focusing). The physical and thermal parameters of corneal tissue and the threshold temperatures for corneal collagen denaturation in different time domains were determined using a water bath and IR laser radiation. The temperature required to coagulate corneal tissue in the millisecond time regime was found to be above 100 degrees C. Based on these results a thermal model was developed to calculate temperature profiles and coagulation zones in space and time for different exposures situations. Model calculations show the possibility to induce deep stromal effects with a spatially nearly homogeneous temperature distribution within the application volume while minimizing adverse effects in the corneal endothelium. !13