Analysis of the cornea-to-PMMA ablation efficiency rate

Abstract

The relative ablation efficiency at different materials (in particular human cornea and poly(methyl methacrylate) (PMMA)) was analysed. A comprehensive model, which directly considers applied correction, including astigmatism, as well as laser beam characteristics and ablative spot properties has been developed. The model further provides a method to convert the deviations in achieved ablation observed in PMMA to equivalent deviations in the cornea. Radiant exposures from about 90 mJ/cm2 to about 500 mJ/cm2 correspond to cornea-to-PMMA ablation ratios of about 9 and about 1.7, respectively (about 7 and 1.3 optically). Super-Gaussian order from simple Gaussian profile to flat-top profile, and for a radiant exposure of 250 mJ/cm2, correspond to cornea-to-PMMA ratios of about 2.3 and about 1.6, respectively (about 1.7 and about 1.2 optically). For a Gaussian beam of 160 mJ/cm2 radiant exposure, a severe overcorrection of +50% in PMMA corresponds only to an overcorrection of +29% on corneal tissue, whereas a moderate overcorrection of +20% in PMMA corresponds to an overcorrection of +12% on corneal tissue. For a severe undercorrection of −50% ablation observed in PMMA, the range for radiant exposures from about 90 mJ/cm2 to about 500 mJ/cm2 correspond to corneal undercorrections of about −14% to about −40%, respectively. The proposed model can be used for calibration, ablation pattern test and development, verification and validation purposes of laser systems used for ablation processes at relatively low cost and would directly improve the quality of results.