Corneal flap thickness in laser in situ keratomileusis using the Moria M2 microkeratome

Purpose: To determine the predictability of flap thickness in laser in situ keratomileusis (LASIK) using the Moria M2 microkeratome and identify factors that may be related to variations in flap thickness. Setting: Laser Vision Correction Center, Bascom Palmer Eye Institute, University of Miami School of Medicine, Miami, Florida, USA. Methods: Charts of 208 patients having same-day bilateral LASIK using the Moria M2 microkeratome were reviewed. Intraoperative pachymetry was performed routinely. The right eye was always treated first. The same suction ring, stop, microkeratome head (110 μm or 130 μm), and blade were used in fellow eyes. Subtraction pachymetry was used to calculate flap thickness. Other collected data included age, keratometry, corneal diameter, and preoperative spherical equivalent (SE). Results: With the 110 μm head and slow translation velocity in both eyes, the mean flap thickness was 151.6 μm ± 24.0 (SD) and 148.5 ± 24.3 μm in the right and left eyes, respectively. With the 110 μm head and fast translation velocity in both eyes, the mean thickness was 136.2 ± 25.5 μm and 132.8 ± 23.5 μm, respectively. With the 130 μm head and fast translation velocity, the mean flap thickness was 145.8 ± 25.4 μm and 139.9 ± 25.5 μm, respectively. Flaps were thinner with fast translation velocity, the 110 μm head, and presumably duller blades used in the left eyes. There was a weak but statistically significant inverse correlation between flap thickness and age and between flap thickness and SE. A stronger correlation was found in flap thickness between right and left eyes. Conclusions: Flap thickness with the Moria M2 microkeratome was variable. Fast translation velocity, a used (presumably duller) blade, and the 110 μm head produced thinner flaps. Given the potential variation in flap thickness (SD 23.5 to 25.5 μm), intraoperative pachymetry might be an adjunctive measure to prevent residual stromal beds that are thinner than planned, especially in patients with high myopia and/or thin corneas.