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

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.