Correlation of laser profilometry scans with clinical results

BACKGROUND: The homogeneity of the ablation profile of excimer lasers can b e disturbed by various reasons. Laser profilometry scans may serve as a pre operative laser quality control if they can be correlated with clinical res ults. METHODS: Four lasers from different manufacturers were calibrated for norma l photorefractive keratectomy, Preoperatively, -3.00 D ablations were perfo rmed on a standardized PMMA Exci-Check. plate. Two- and three-dimensional s urface scans were taken from the PMMA samples. The optical zone and the abl ation depth were measured. Surface roughness and regularity of the ablation profile were compared. The PMMA ablation depth was plotted with the postop erative refraction, Surface regularity was correlated to loss of spectacle- corrected visual acuity. RESULTS: The ablation depth on PMMA changed with time in all four tested la sers. For one laser we measured an ablation depth between 6 and 9 mu m whic h we could correlate to a postoperative refraction of -0.50 to +2.00 D at 2 months after PRK. Surface roughness of these different lasers different si gnificantly from each other. Asymmetric ablation profiles produced a loss o f spectacle-corrected visual acuity. CONCLUSION: This study indicates there may be a correlation between results of laser surface profilometry scans and clinical outcomes. A more sophisti cated quality control than currently available seems possible and is necess ary, Laser profilometry (Exci-Check) provided detailed information about th e laser and the ablation conditions, and may help to avoid undesirable clin ical outcomes from ablation profile irregularities.