Computational study for temperature distribution in ArF excimer laser corneal refractive surgeries using different beam delivery techniques.

Abstract

Refractive errors are the most common causes of vision impairment worldwide and laser refractive surgery is one of the most frequently performed ocular surgeries. Clinical studies have reported that approximately 10.5% of patients need an additional procedure after thesurgery. The major complications of laser surgeryare over/undercorrection and dry eye. An increase in temperature may be a cause for these complications. The purpose of this study was to estimate the increase in temperature during laser refractive surgery and its relationship with the complications observed for different surgical techniques. In this paper, a finite element model was applied to investigate the temperature distribution of the cornea when subjected to ArF excimer laser at a single spot using various beam delivery systems (broad beam, scanning slit, and flying spot). The Pennes bio-heat equation was used to predict the temperature values at different laser pulse energies and frequencies. The maximum temperature increase by ArF laser ([Formula: see text] frequency and [Formula: see text] pulse energy) at a single spot was [Formula: see text] for [Formula: see text] diopter correction ([Formula: see text] of ablation of corneal stroma) using broad beam, scanning slit, and flying spot beam delivery approaches respectively. The peak temperature due to a single pulse was estimated to be [Formula: see text]. Although the peak temperature (sufficient energy to break intermolecular bonds) exists for a very short time ([Formula: see text]) compared to the thermal relaxation time ([Formula: see text]), there is some thermal energy exchange between corneal tissues during a laser refractive surgery. Heating may cause collagen denaturation, collagen shrinkage, and more evaporation and hence proposed to be a risk factor for over/undercorrection and dry eye.