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

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 the surgery. The major complications of laser surgery are over/under correction 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 (\(500\mathrm{ Hz}\) frequency and \(0.5\mathrm{ J}\) pulse energy) at a single spot was \(33.94^{\circ} \mathrm{C}, 15.86^{\circ} \mathrm{C}, 12.48^{\circ} \mathrm{C}\) for \(6\) diopter correction (\(65.4 \upmu \mathrm{m}\) 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 \(234.14 ^{\circ} \mathrm{C}\). Although the peak temperature (sufficient energy to break intermolecular bonds) exists for a very short time (\(10-30\mathrm{ ns}\)) compared to the thermal relaxation time (\(2000-10,000 \upmu \mathrm{s}\)), 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/under correction and dry eye.