To the Editor.
—The 193-nm wavelength generated by the argon fluoride excimer laser precisely ablates corneal tissue without evidence of adjacent thermal damage.1 Lower-energy excimer wavelengths, including 248, 308, and 351 nm, have been investigated and found to produce a zone of adjacent thermal damage that increases with the wavelength.The mechanism by which far ultraviolet (UV) energy interacts with corneal tissue is controversial and poorly understood. Srinivasan and colleagues2 have suggested that highly energetic far UV photons (6.4 eV at 193 nm) directly break the intramolecular bonds that link the collagen polymer together. This process is dependent on high corneal absorption of the wavelength and sufficient photon energy to induce bond disruption.2 Other possible mechanisms include ultrafast thermal events in which heating is confined to a small volume of corneal tissue that is vaporized before significant thermal diffusion into surrounding cornea occurs.We irradiated human cadaver corneas
Thompson KP, Trentacoste J, Parrish RK, Berman MR. Corneal Photoablation by Far Ultraviolet Lasers. Arch Ophthalmol. 1987;105(3):312–313. doi:10.1001/archopht.1987.01060030026005
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