MEASUREMENT AND MODELING OF THERMAL TRANSIENTS DURING ER-YAG LASER IRRADIATION OF VITREOUS

Background and Objective: We investigated the transient thermal behavi or of vitreous in order to understand the local thermal effects of las er output, and to predict the potential for unintentional injury durin g Er:YAG laser vitreoretinal surgery. Study Design/Materials and Metho ds: The output of a free-running Er:YAG laser (2.94 mu m, 300 mu s FWH M) was delivered through a fiberoptic and applied to en bloc samples o f bovine vitreous. Temperature was measured with ultrafine thermocoupl es. Results: For 6 mJ pulse energy at 10 Hz, a temperature rise of 20 degrees C is measured 500 mu m from the laser tip. The temperature ris e is localized with a rapid fall-off greater than I mm from the energy source. At constant time-averaged laser power, the temperature profil e is independent of repetition rate. Our finite-difference model gener ates results qualitatively consistent with measured data and allows fo r investigation of the influence of thermophysical parameters on heat transfer. Conclusion: Thermal injury to ocular structures should be Li mited during intravitreal application of Er:YAG laser energy. (C) 1996 Wiley-Liss, Inc.