The clinical feasibility of photorefractive keratectomy depends on the surface structure of the ablated cornea. Two factors that influence the remodeled surface are the homogeneity of the energy distribution and the properties of the laser source (energy and wavelength). Currently, the homogeneity of the beam is difficult to control. The second factor, laser source properties, was the focus of this study. We investigated the effect of laser wavelength and energy by analyzing the reaction products of photoablation. We monitored the fragments produced by UV-laser ablation of human corneas using mass spectroscopy in the range of 0 to 100 atomic mass units. At 248 nm (KrF), average photon energy was 5 mJ/cm2, increased to 90 mJ/cm2 by intervals of 5 mJ/cm2. At 193 nm (ArF), photon energy was increased by the same interval from 5 mJ/cm2 to 80 mJ/cm2. Our experiments showed that there was a fluence threshold of approximately 40 mJ/cm2 at 193 nm (ArF) and 50 mJ/cm2 at 248 nm (KrF). Exceeding this threshold led to sudden increases in the number and relative intensity of fragment peaks in mass spectroscopy. This indicates the onset of multiple-photon processes and effective photochemical breakdown. There was a significant difference between both wavelengths in the distribution of mass peaks, indicating higher ionization power at 193 nm.

56 human eyes were stored in a moist chamber from 0 to 4 days at +4°C. 20 human corneal buttons with a scleral rim were stored in the M-K medium for 5 and 7 days at +4°C. After this procedure in both series the temperature reversal effect was measured and the living endothelial cells were counted after being stained with trypan blue and rose bengal. All eyes showed a typical swelling-shrinking phenomena but after 4 days in a moist chamber this effect was definitely less characteristic than in all other periods of storage time. In respect to the endothelial cell counts 5 day M-K medium storage corresponds to 2 day moist chamber storage, and 7 day M-K storage is comparable to 3 day moist chamber storage. The total survival time of the endothelial cells in both series is almost equal.

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