Thermal and mechanical damage of corneal tissue after free-running and Q-switched mid-infrared laser ablation

摘要

Laser ablation of corneal tissue by mid-infrared laser radiation was studied in dependence of the laser wavelength and the pulse duration. The thermally and mechanically laser induced damage was determined by light microscopy (LM) and scanning electron microscopy (SEM). Fresh porcine eyes were irradiated with three different lasers: Er:YAG ($lambda $EQ 2.94 $mu@m), Er:YSGG ($lambda $EQ 2.79 $mu@m) and Ho:YAG ($lambda $EQ 2.1 $mu@m). The experiments were performed with both, free running (pulse duration $tau $EQ 200 $mu@s) and Q-switched pulsed ($tau $EQ 100 ns) lasers. The extent of thermally damaged tissue was found to be the same for Er:YAG and Er:YSGG lasers: 8 - 45 $mu@m and 2 - 10 $mu@m, with the long and the Q-switched pulses, respectively. The Ho:YAG laser induced coagulation zones were 200 - 600 $mu@m thick in the free running and 40 - 80 $mu@m in the Q-switched mode. The ablation efficiency of Er-lasers was between 4 and 13 times higher than that of the Ho:YAG.