Correlation of laser profilometry scans with clinical results

The homogeneity of the ablation profile of excimer lasers can be disturbed by various reasons. Laser profilometry scans may serve as a preoperative laser quality control if they can be correlated with clinical results.

Four lasers from different manufacturers were calibrated for normal photorefractive keratectomy. Preoperatively, -3.00 D ablations were performed on a standardized PMMA Exci-Check plate. Two- and three-dimensional surface scans were taken from the PMMA samples. The optical zone and the ablation depth were measured. Surface roughness and regularity of the ablation profile were compared. The PMMA ablation depth was plotted with the postoperative refraction. Surface regularity was correlated to loss of spectacle-corrected visual acuity.

The ablation depth on PMMA changed with time in all four tested lasers. For one laser we measured an ablation depth between 6 and 9 microns which 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 significantly from each other. Asymmetric ablation profiles produced a loss of spectacle-corrected visual acuity.

This study indicates there may be a correlation between results of laser surface profilometry scans and clinical outcomes. A more sophisticated quality control than currently available seems possible and is necessary. Laser profilometry (Exci-Check) provided detailed information about the laser and the ablation conditions, and may help to avoid undesirable clinical outcomes from ablation profile irregularities.