The effect of corneal hydration on corneal ablation rate at 193nm and 213nm

Abstract

Abstract Purpose The ablation rate of corneal tissue depends primarily on the fluence of the laser and corneal hydration. It was the purpose of the study to compare the dependence of the ablation rate on corneal hydration for two different laser wavelengths (193 and 213‐nm). Methods ArF Excimer laser (Allegretto, Wavelight) with a wavelength of 193nm and Nd:YAG CustomVis laser with a wavelength of 213nm were used for the study. Corneal discs were harvested from porcine eye within 24 hours post‐mortem. Corneal epithelium was removed with a blunt spatula. The disks received ablation equivalent to the ablation of 100 microns at a circular zone having a diameter of 7mm. Before and after ablation, each disk was weighted and subsequently dried in order to calculate its dry mass and therefore hydration during ablation. In order to test the ablation rate at different hydrations, the disks were ablated at different time intervals fooling their preparation. The hydration ranged from 66 to 80% w/w. Results The ablated mass showed a positive linear correlation with hydration for both lasers. The corresponding normalised dry mass, which is more critical for the accuracy of refractive corrections, exhibited a negative linear correlation with hydration with similar slopes for the two lasers tested (‐0,0651 for the 193nm and ‐0,0568[hydration‐1] for the 213nm). Conclusion Results of this study reveal the similar behaviour in the dependence of ablation rate from the hydration of cornea at the 193‐ and 213‐nm laser wavelengths.