The Effects of Ambient Temperature and Ablation Interruption on Thermal Load During Excimer Laser Ablation.

Purpose: To analyze the effects of ablation interruption on ablation depths and clinical refractive outcomes to characterize the impact of ambient temperature changes and ablation interruption on ocular surface temperature (OST) during excimer laser ablation.

Methods: This prospective study was conducted on laser ablations in polymethylmethacrylate (PMMA) plates and porcine corneas to simulate laser in situ keratomileusis (LASIK) treatments using the EX500 laser (Alcon Laboratories, Inc) at ambient temperatures of 18, 20, and 22 °C. Ablation interruption was performed for 1, 2, 3, 4, and 5 seconds at the 10th second of the treatment of -9.00 diopters (D) of myopia. OST changes were recorded using infrared thermography, and the ablation depth of each PMMA plate was measured using a high-precision contact micrometer. Postoperative outcomes of patients were evaluated based on the refractive results under varying ablation interruption durations.

Results: Both the PMMA plates and porcine corneas exhibited significant photothermal effects. Under -9.00 D excimer laser ablation at 18, 20, and 22 °C, the OST reached 80.10 ± 0.22, 82.26 ± 0.99, and 84.01 ± 1.46 °C for PMMA plates and 28.3 ± 0.40, 29.0 ± 0.59, and 30.8 ± 0.43 °C for porcine corneas, respectively. Laser ablation interruption significantly reduced the photothermal peak in PMMA plates and porcine corneas. The ablation depth of PMMA decreased as the ambient temperature increased. The ablation depths of the PMMA plates were less stable with ablation interruptions of 3 and 4 seconds, and the sphere and spherical equivalent (SEQ) refraction was significantly higher than that without ablation interruption.

Conclusions: Changes in the ambient temperature can affect the thermal load during excimer laser ablation. Ablation interruptions reduce the thermal load and increase the ablation depth, which in turn influences clinical refractive outcomes.