Corneal ablation research at the FDA

Summary form only given. Although excimer laser refractive surgery has been available in the United States for a year-and longer elsewhere-the fundamental mechanisms of photoablation are still not fully understood. Consequently, the motivation for corneal ablation research at FDA has been to more fully describe the underlying laser-tissue interactions occurring in ultraviolet laser photoablation. Our investigations have explored the implications of laser-induced-fluorescence on the lens, DNA damage due to ultraviolet radiation and free-radical production. Studies have also been performed to evaluate the pulse-to-pulse stability of ablation, "incubation", and the effects of ablation site hydration. Time-resolved reflectivity and transmission measurements have demonstrated dynamic alteration of the optical properties of the ablation site during the laser pulse. Characteristics of the ablation plume including particle size, velocity and volume fraction have been determined by time-resolved Mie scattering measurements. Also, the values for the index of refraction and absorption coefficient (small-signal) of cornea have been obtained by critical angle reflectometry. The results of these studies are reviewed and their clinical implications discussed.