Measurement and modeling of thermal transients during Er:YAG laser irradiation of vitreous.

Overview

BACKGROUND AND OBJECTIVE: We investigated the transient thermal behavior of vitreous in order to understand the local thermal effects of laser output, and to predict the potential for unintentional injury during Er:YAG laser vitreoretinal surgery. STUDY DESIGN/MATERIALS AND METHODS: The output of a free-running Er:YAG laser (2.94 microns, 300 microseconds FWHM) was delivered through a fiberoptic and applied to en bloc samples of bovine vitreous. Temperature was measured with ultrafine thermocouples. RESULTS: For 6 mJ pulse energy at 10 Hz, a temperature rise of 20 degrees C is measured 500 microns from the laser tip. The temperature rise is localized with a rapid fall-off greater than 1 mm from the energy source. At constant time-averaged laser power, the temperature profile is independent of repetition rate. Our finite-difference model generates results qualitatively consistent with measured data and allows for investigation of the influence of thermophysical parameters on heat transfer. CONCLUSION: Thermal injury to ocular structures should be limited during intravitreal application of Er:YAG laser energy.