Corneal temperature changes during photorefractive keratectomy using the Laserscan 2000 flying spot laser.

PURPOSE: To evaluate the thermal variations during photorefractive keratectomy (PRK) induced by a Laserscan 2000 flying spot excimer laser.

METHODS

Thermal changes during PRK were recorded using a non-contact infrared thermometer on 58 eyes with an attempted correction ranging from -1.25 to -9.00 D. The eyes were randomly divided into two groups to test the thermal effects of two different ablation scan techniques: sequential and randomized modes. Thermal measurements were also performed during myopic ablations on polymethylmethacrylate (PMMA) test plates.

RESULTS

On PMMA plates, a significant relationship between the amount of attempted myopic correction and thermal changes was established (P=.017 in sequential mode and P=.007 in randomized mode); this was not established for human eyes. With the sequential mode, an unexpected cooling effect after PRK was reported for each myopia subgroup (P=.003 in the low and high myopia subgroups, P<.001 in the medium myopia subgroup). With the randomized mode, the cooling effect was detected only for low amounts of myopia.

CONCLUSION

Despite a high repetition rate, the Laserscan 2000 flying spot laser minimized thermal shock. In comparison with randomized (nonsequential) pulse application, sequential pulsing showed no increase in the thermal loading of corneas. In fact, a cooling effect during PRK was produced.