Comparison of Laser In Situ Keratomileusis Flap Morphology and Predictability by WaveLight FS200 Femtosecond Laser and Moria Microkeratome: An Anterior Segment Optical Coherence Tomography Study

Abstract

Purpose: To evaluate laser in situ keratomileusis (LASIK) flap thickness predictability and morphology by femtosecond (FS) laser and microkeratome (MK) using anterior segment optical coherence tomography.

Methods: Fifty-two candidates for the LASIK procedure were stratified into two groups: FS laser-assisted (Allegretto FS-200) and MK flap creation (Moria 2). Flap thickness was determined at five points. The side-cut angle was measured in three directions at the margin interface. LASIK flap assessment was performed one month postoperatively by Spectralis anterior segment optical coherence tomography.

Results: Fifty-two patients (93 eyes) were recruited; 49 eyes were stratified to the FS group and 44 eyes to the MK group. The FS group had relatively even flap configurations, and the MK group had meniscus-shaped flaps. Mean differences between planned and actual flap thickness were 12.93 ± 8.89 and 19.91 ± 5.77 μm in the FS and MK groups, respectively. In thin flaps (100 to 110 μm), there was a significant disparity between the two groups (7.80 ± 4.71 and 19.44 ± 4.46 μm in the FS and MK groups, respectively). However, in thicker flaps (130 μm), comparable flap thickness disparity was achieved (18.54 ± 9.52 and 20.83 ± 5.99 μm in the FS and MK groups, respectively). Mean side-cut angle was 74.29 ± 5.79 degrees and 32.34 ± 4.94 degrees in the FS and MK groups, respectively.

Conclusions: Comparable flap thickness predictability was achieved in thicker flaps (130 μm), while the FS laser technique yielded a more predictable result in thinner flaps (100 to 110 μm). Different flap morphology was observed in meniscus flaps in MK-LASIK and flap morphology in FS-LASIK.

Keywords: Anterior segment optical coherence tomography; Flap morphology; Laser in situ keratomileusis.

Fig. 1. Laser in situ keratomileusis (LASIK) flap side-cut angle and edge outline in (A) microkeratome-assisted LASIK and (B) femtosecond laser-assisted LASIK groups by anterior segment optical coherence tomography.

Fig. 2. Average flap thickness in femtosecond laser-assisted laser in situ keratomileusis (LASIK) and microkeratome-assisted LASIK groups as measured in five different locations (centrally, 1 mm nasally and temporally, 2.5 mm nasally and temporally across horizontal meridian). The difference between two groups is more evident in planned flap thickness of 100 to 110 µm. (A) Planned flap thickness (pooled date), (B) planned LASIK flap (130 µm), and (C) planned LASIK flap (100 to 110 µm). N = nasal; T = temporal.

Fig. 3. Frequency of distribution of postoperative (microkeratome-assisted laser in situ keratomileusis [MK-LASIK] and femtosecond laser-assisted laser in situ keratomileusis [FS-LASIK]) manifest spherical equivalent.