Changes in custom biomechanical variables after femtosecond laser in situ keratomileusis and photorefractive keratectomy for myopia

PURPOSE: To analyze changes in new biomechanical descriptors with myopic femtosecond laser assisted laser in situ keratomileusis (LASIK), compare them with the biomechanical response after photorefractive keratectomy (PRK) with similar levels of myopic ablation, and evaluate correlations between changes in custom variables and biomechanically relevant variables. SETTING: Cleveland Clinic, Cleveland, Ohio, USA. DESIGN: Cohort study. METHODS: Custom biomechanical variables from the Optical Response Analyzer were assessed preoperatively and 1 and 3 months postoperatively. Differences between preoperative values and postoperative values were determined. Intraindividual change (preoperative value minus postoperative value) was calculated and compared with changes after PRK. The correlation of the change in each custom biomechanical variable with the preoperative central corneal thickness, residual stromal bed tissue ablated, and percentage of tissue depth altered was also studied. RESULTS: The study enrolled 156 eyes of 156 consecutive patients. Fifteen variables changed significantly after femtosecond myopic LASIK and were stable postoperatively because no significant difference was shown between 1-month values and 3-month values. Comparison of the changes in biomechanical variables between LASIK and PRK eyes showed no significant differences. Surgical changes in several custom biomechanical variables correlated with the percentage of tissue depth altered. CONCLUSIONS: The results provide the first reference values for a more comprehensive panel of indicators of the biomechanical response to myopic LASIK and PRK. Changes in custom variables reflected a consistent decrease in corneal biomechanical resistance to deformation after myopic femtosecond LASIK and PRK. For comparable attempted corrections, biomechanical changes were comparable between femtosecond laser assisted LASIK and PRK. (C) 2014 ASCRS and ESCRS