Repeatability of laser in situ keratomileusis flap thickness measurement by Fourier-domain optical coherence tomography

Abstract

PURPOSE: To evaluate the repeatability of Fourier-domain optical coherence tomography (OCT) measurements of the thickness of femtosecond laser-created laser in situ keratomileusis (LASIK) flaps.SETTING: Doheny Eye Institute, University of Southern California, Los Angeles, California, USA.DESIGN: Case series, evaluation of diagnostic technology.METHODS: in this consecutive series, Fourier-domain OCT (RTVue) was used to measure flap thickness 1 week after LASIK. Flaps were created with a Pulsion 60 kHz femtosecond laser programmed for 110 mu m flap thickness. Each eye was scanned 2 times with a radial pachymetry pattern and 1 time with a horizontal line scan. Flap thicknesses were measured at 6 positions across the corneal flap (ie, +/- 0.5 mm, +/- 1.5 mm, and +/- 2.5 mm from the center on the horizontal and vertical meridians). the within-grader flap thickness repeatability and between-grader reproducibility were calculated by pooled standard deviations (SDs).RESULTS: Twenty-one eyes were measured. the mean flap thickness measurements were highly predictable at all positions. Thickness SDs varied from 5.3 to 9.5 mu m and uniformity, from 121.7 to 126.5 mu m. the within-grader repeatability was 3.3 to 6.4 mu m based on the same image measured at different times and 4.7 to 7.4 mu m for different images. the between-grader reproducibility was 4.0 to 9.0 mu m. There was no statistically significant asymmetry between the nasal side and the temporal side, the superior side and the inferior side, or the pericentral area and the central area of the corneal flap.CONCLUSIONS: the femtosecond laser created LASIK flaps with uniform and predictable thicknesses. Fourier-domain OCT gave highly repeatable flap-thickness measurements.