Factors influencing corneal flap thickness in laser in situ keratomileusis with a femtosecond laser.

Over the past decade, laser in situ keratomileusis (LASIK) has become the most common refractive procedure for the correction of refractive errors. Consistency and predictability of corneal flap thickness is crucial in both planning and in producing successful LASIK outcomes. Complications associated with thin flaps include flap slippage, striae, irregularity, astigmatism, buttonholes, free caps, and corneal haze. Thicker flaps cause decreased stromal-bed thickness, which increases the risk for biomechanical corneal changes and iatrogenic corneal ectasia [1-4]. Few studies have attempted to find a correlation between preoperative variables and corneal-flap thickness with the mechanical microkeratome. Yildirim et al. [5] found a low correlation with preoperative corneal thickness and no correlation with preoperative keratometry when using the mechanical microkeratome. Giledi et al. [6] reported a correlation between preoperative spherical-equivalent refraction and flap thickness, and a paradoxical finding of thinner flaps in patients with thicker corneas using the mechanical microkeratome. Current mechanical microkeratomes have a very good performance record; however, in a few cases, complications can occur during the microkeratome pass and flap cut. Femtosecond lasers offer an alternative to mechanical cutting and can provide additional features that affect flap morphology. Studies by Krueger and Dupps [7] and Alio and Pinero [8] found a planar-flap profile for femtosecond-laser-created flaps versus a meniscus-flap profile for microkeratome flaps. A meniscus flap extends deeper in the periphery and is shallower in the center of the flap, while a planar flap has the same thickness across its entirety. Despite the improved flap-thickness predictability with the femtosecond lasers compared with the conventional microkeratome, unexpectedly thinner or thicker flaps sometimes occur with the femtosecond lasers and can lead to surgical complications [9]. The main aim of this study was to evaluate preoperative variables and flap thickness in eyes having flap creation with the femtosecond-laser-assisted LASIK.