IN-VITRO MEASUREMENTS OF CYTOTOXIC EFFECTS OF 193 NM AND 213 NM LASER-PULSES AT SUBABLATIVE FLUENCES

Background and Objective: The frequency-quintupled q-switched Nd:YAG l aser is being studied as an alternative to the ArF excimer laser for p hotorefractive procedures. The present report describes two experiment s comparing biologic effects of these laser devices. Study Design/Mate rials and Methods: Bovine corneas were irradiated with subablative las er pulses in Liquid nitrogen and analyzed by electron paramagnetic res onance spectroscopy to assess free radical production. Aqueous bacteri al suspensions were irradiated with low-intensity laser pulses and ass ayed for cell survival. Results: Electron paramagnetic resonance spect ra were very similar in both amplitude and shape for exposure at the t wo wavelengths. Bacterial survival was markedly less for 213 nn irradi ation than 193 nn exposure and displayed a different dependence on cum ulative exposure. Conclusion: Free radical production by 213 nn laser exposure is quite comparable to that seen previously for 193 nm irradi ation. However, cell lethality appears to be significantly greater at the longer ultraviolet wavelength. This difference may contribute to c omplications observed after corneal photoablation with the 213 nn devi ce. (C) 1997 Wiley-Liss, Inc.