Effects of Laser Repetition Rate on Corneal Tissue Ablation for 193-NM Excimer Laser Light

Abstract

Purpose:: Clinical excimer laser refractive surgery systems are continually evolving to improve accuracy and precision, including efforts to shorten the treatment duration by enhancing laser repetition rates. However, a complete understanding of the physics and mechanisms of corneal ablation and the potential role of laser repetition rate remains a topic of research. A better understanding of this issue may lead to more efficient refractive procedures.

Methods:: 193-nm ArF excimer laser ablation experiments were conducted using enucleated whole bovine eyes. Planar laser light scattering and 193-nm probe laser beams were used to examine the dynamics of ablation material ejection, including solid (i.e. particulate) phase and gas phase components. In addition, a precise white-light interferometry technique was used to directly assess corneal ablation profiles for various laser repetition rates between 60 and 400 Hz.

Results:: Complete ablation crater profiles were compared for various overall refractive corrections. Based on maximum ablation depth, no statistical difference was found between corneal ablation rates performed at 60 and 400 Hz, namely 23.6 microns (2.0) at 60 Hz versus 23.1 microns (2.9) at 400 Hz. The ejection of bulk debris was found to dissipate on a time-scale less than the laser shot-to-shot difference for all laser repetition rates, while an apparent gas-phase component of the ablation products was found to be comparable at all repetition rates.

Conclusions:: Investigation of the relative effects of excimer laser repetition rate on the overall corneal ablation rate revealed no measurable effect on laser ablation profiles for corneal tissue under conditions typical of refractive procedures. These results are consistent with direct measurement of the ablation product dynamics. The experiments suggest that enhancement in excimer laser repetition rates may be practical, and thereby justify the pursuit of additional studies.

Keywords: laser • refractive surgery: LASIK • refractive surgery: comparative studies