Optical low coherence reflectometry for noncontact measurements of flap thickness during laser in situ keratomileusis

Abstract

Objective There is growing evidence that iatrogenic keratectasia after laser in situ keratomileusis (LASIK) for high corrections occurs more frequently than initially assumed, and that it may result from larger variation in flap thickness. Design Consecutive noncomparative case series Participants Thirty-four patients who underwent LASIK for myopia and astigmatism (first treatment group) and 10 patients who received re-LASIK (retreatment group). Methods Central corneal thickness and thickness of the lamella during LASIK were determined by optical low coherence reflectometry (OLCR) and contact ultrasound pachymetry. Main outcome measures Thickness of the flap and its standard deviation, as well as its correlation with age, sphere, cylinder, corneal thickness, intraocular pressure, and corneal refractive power (K-readings). Results The mean flap thickness of the first treatment group determined by OLCR was 130 ± 29 μm; the 95 percentile was 169 μm and the 5 percentile was 86 μm. The flap thickness was not correlated with any of the investigated demographic or refractive parameters. The mean flap thickness of the retreatment group was 152 ± 14 μm; the 95 percentile was 175 μm and the 5 percentile was 137 μm. Thus, the flap thickness of the retreatment group was significantly thicker compared with the first treatment group ( P < 0.001). Conclusions Optical low coherence reflectometry (OLCR) was shown to be an appropriate alternative to ultrasonic preoperative and intraoperative corneal pachymetry in laser assisted in situ keratomileusis. The lack of correlation between achieved flap thickness and preoperative clinical data, such as corneal thickness, corneal curvature, intraocular pressure, and refraction, emphasizes the importance of measuring flap thickness and corneal bed thickness during surgery.