Effect of time sequences in scanning algorithms on the surface temperature during corneal laser surgery with high-repetition-rate excimer laser

Abstract

High-repetition-rate excimer laser systems require spot sequences with optimized temporal and spatial spot distribution to minimize the increase in ocular surface temperature. An ocular surface temperature increase will always occur depending on the amount of refractive correction, the type of ablation profile, the radiant exposure, and the repetition rate of the laser system.

Evaluation of thermal load during laser corneal refractive surgery using infrared thermography

“…In order to optimize correction results, sophisticated scanning algorithms are under development, including customized treatments, based on a sequential application of spacial distributed laser pulses [1,2]. Each of these pulses deliberately ablates a small amount of corneal tissue, but contributes also to the thermal load of the tissue, as an increase of the ocular surface temperature can be observed during treatment of the eye.…”

“…Unlike conventional pulse infrared thermography which uses surface-wide heating [15], this method uses local pulse heating and presents information of the thermal load on a global basis rather than on a local basis. This actually is of special interest for the optimization of time sequences and lateral distribution of laser pulses which control OST during corneal laser surgery as recently demonstrated by Mrochen et al [1]. Though the method is most often used and accuracy becomes the more important the lower the thermal load is, its constraints are scarcely discussed and the implications of the spatial and temporal resolution of the measurement system have been not often presented.…”

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

“…18,19 Critical asymmetric heating of the cornea can be avoided by optimum distribution of the laser spots. In a study by Mrochen et al, 19 the highest mean temperature increase using this 1000 Hz excimer laser was 10.11 K. Therefore, the 11 C limit Bende et al 15 recommend for corneal heating during ablation was not exceeded. However, in the study by Mrochen et al, the maximum temperature rise was 15.36 K in eyes having a À9.00 D correction.…”

“…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.…”

Corneal Surface Asphericity, Roughness, and Transverse Contraction after Uniform Scanning Excimer Laser Ablation

“…22 Some newer lasers running in excess of 1000 Hz and 500 mJ/cm 2 are capable of reaching maximum temperature increases of almost 20°C. 36 Thermal energy denatures the triple-helix structure of the corneal collagen, creating a contractile force along its lengthwise dimension. 37 Thermally denatured collagen can shrink between 8% and Ͼ30% of its original length, as seen in CO 2 laser studies.…”