Laser-induced photodecomposition of amino acids and peptides: extrapolation to corneal collagen

Recent studies on the laser photochemistry of aromatic and aliphatic amino acids and small peptides in neutral aqueous solution are described. We report on major parameters such as photoionization and photodecomposition quantum yields for the cases of direct (and indirect) photolysis. Although four different UV laser sources were used, the impact is made on 193-nm-induced photoprocesses. The relative probabilities of photochemical damage of specific residues are estimated. It is shown that the peptide bond is likely to be the main target in collagen. Its scission could be the most important photochemical reaction taking place at 193-nm laser irradiation of the cornea. We have found strong arguments in favor of the ablative photodecomposition mechanism of photorefractive keratectomy.