Intrastromal cutting effects in rabbit cornea using femtosecond laser pulses

摘要

In this work the dependence of the threshold energy and pulse duration for photodisruption was studied between 100 and 1500 femtoseconds using an erbium fibre laser system with subsequent chirped pulse amplification in a titanium-sapphire system. Cutting effects were analysed in animal specimens like rabbit cornea and porcine eye globes. To perform intrastromal cuts, the laser beam was guided through a computer controlled delivery system. The treated tissue was analysed by histological sections and by means of light and electron microscopy. Pressure transients were measured at the endothelium during the cutting procedure. Bubble formation and dynamics were studied using flash photography. The resulting gas bubbles were analysed to their content, and photodissocation could be noticed. As a result of these studies a set of optimised parameters for pulse duration, scanning algorithm, pulse energy and the focusing and beam delivery system could be found. The thermal damage zone in the irradiated tissue was found to be smaller than 1 mum and maximum pressure transients at the endothelium could be determined to be in the range of some hundred millibars. Moreover, performing of intrastromal cuts and creation of a lenticule for achieving a refractive effect in the eye was demonstrated. The investigations show, that fs-pulses are a very precise tool for refractive surgery.