Effects of laser repetition rate on corneal tissue ablation for 193‐nm excimer laser light

Abstract

In summary, investigation of the relative effects of excimer laser repetition rate on the overall corneal ablation metrics revealed no measurable difference under conditions typical of clinical refractive procedures. This study suggests that increases in ArF laser repetition rates for clinical applications (up to approximately 400 Hz) appear feasible.

Effect of 3 excimer laser ablation frequencies (200 Hz, 500 Hz, 1000 Hz) on the cornea using a 1000 Hz scanning-spot excimer laser

“…In a recent study, Shanyfelt et al 22 examined the potential effects of laser repetition rates on corneal tissue. They found no observable effects in a comparison between the repetition rates 60 Hz and 400 Hz.…”

“…21 Denaturing and coagulation of collagen as a sign of thermal damage can be observed on microscopy and manifests as an aggregation of collagen fibrils and disruptions in the collagen structure. 22 Possible changes in the efficiency of the ablation should also be taken into consideration when increasing the repetition rate of an excimer laser. 21 The aim of this experimental study was to assess the histopathologic characteristics of human and porcine cadaver eyes that were treated using a prototype 1000 Hz excimer laser system and 1 of 3 ablation frequencies.…”

First clinical results of epithelial laser in situ keratomileusis with a 1000 Hz excimer laser

“…Nevertheless, an increase in corneal surface temperature will always occur depending on the type and amount of refractive correction, the radiant exposure, and the repetition rate of the excimer laser. 19 Recently, Shanyfelt et al 20 examined the potential effects of laser repetition rates on corneal tissue. There were no observable effects with rates of 60 Hz and 400 Hz.…”

“…The authors also detected a relatively smooth corneal surface and normal structure in the deeper corneal layers, which agrees with the findings in our previous study in which we used the same or higher repetition rates. Shanyfelt et al 20 estimated the critical laser repetition rate for 193 nm excimer laser ablation to be in the range of kilohertz based on the fact that the thermal relaxation time might be estimated to be on the order of tens of microseconds due to the high absorption coefficient. The present study confirms that visual outcomes are not negatively affected when a 1000 Hz excimer laser is used.…”

Optimum Laser Beam Characteristics for Achieving Smoother Ablations in Laser Vision Correction

“…12 Several mathematical models have been proposed in the recent times, particularly for laser tissue interaction in refractive surgery, in the form of modifications in the Lambert-Beer law. [13][14][15][16][17][18][19][20][21][22][23][24] Despite the various modeling approaches comparing the overall predicted performance of laser platforms, an extensive analysis of the impact of individual laser beam characteristics like spot energy, spot diameter, super Gaussian order, truncation radius, spot geometry, spot overlap, and lattice geometry on ablation smoothness is not existing in the literature, to the best of our knowledge. These laser beam characteristics may individually affect the ablation smoothness; for example, truncating the flanks of the beam profile to avoid thermal loads, preferring flatter beams for a higher ablation volume per laser pulse, preferring smaller spot sizes to increase the resolution for ablating fine structure, preferring lower pulse energy for imparting lesser energy on the cornea (but being more sensitive to perturbations), or preferring higher pulse energy for achieving stability but at the expense of higher thermal load, may all impact the ablation smoothness either constructively or destructively.…”