STUDY OF CORNEAL ABLATION WITH PICOSECOND LASER-PULSES AT 211 NM AND 263 NM

Background and Objective: Corneal ablation has been studied by picosec ond laser pulses in the far-UV region. Study Design/Materials and Meth ods: Laser pulses of 25 ps duration at 211 nn and 263 nm wavelengths a nd a 1 kHz repetition rate have been used to ablate human and rabbit c orneas. The dependence of the etch rate on laser fluence has been meas ured at both wavelengths. The collateral tissue damage has been invest igated by electron microscopy. Results: The ablation threshold for hum an cornea is determined to be about 3.0 mJ/cm(2) at 211 nm, while the thresholds for rabbit cornea are about 2.3 mJ/cm(2) at 211 nm and 8.0 mJ/cm(2) at 263 nm. The slopes of the ablation curves and the dimensio ns of the damage zones have also been determined. Conclusion: We compa re these results to the existing data on corneal ablation by nanosecon d UV pulses and discuss the deficiency of the photochemical model. Exp erimental results are analyzed in terms of a model that features plasm a ablation assisted by chromophore absorption. (C) 1996 Wiley-Liss, In c.