Corneal flap thickness and topography changes induced by flap creation during laser in situ keratomileusis

Purpose: To determine the corneal flap thickness profile produced by 3 microkeratomes and the topographic changes induced by flap creation in laser in situ keratomileusis (LASIK). Setting: Cornea and Refractive Surgery Unit, Instituto de Microcirugfa Ocular de Barcelona, Autonoma University, Barcelona, Spain. Methods: In this prospective consecutive nonrandomized comparative study, patients were divided into 2 groups. In Group 1 (75 eyes), 3 microkeratomes were used: Moria LSX One, Moria M2, and Amadeus (AMO); 25 eyes per microkeratome. Pachymetry was measured with a DGH pachymeter in the center of the cornea and 3.0 mm from the center at 4 cardinal points (superior, inferior, nasal, and temporal; 3 measurements at each point) before and after the cut. The flap thickness in each sector was calculated by subtracting the mean post-flap corneal thickness from the mean pre-flap corneal thickness. In Group 2 (33 eyes), the M2 microkeratome with a 130 mum plate was used to create a superotemporal hinged flap (9 eyes) or a superonasal hinged flap (24 eyes). The topographic change induced by the microkeratome cut was evaluated using 4 sequential data acquisitions by the Keratron Scout topographic unit (Optikon) before and immediately after the cut (before laser ablation). Cardinal and oblique astigmatism and change in the axis were calculated by vectorial analysis of the simulated keratometry. Topographic Zernike analysis was performed in a subgroup. Results: With the LSX One microkeratome, the mean flap thickness was 151.7 mum centrally, 161.9 mum superiorly, 151.4 mum inferiorly, 156.1 mum temporally, and 167.5 mum nasally. There was no statistically significant difference between the areas studied (P<.05). With the M2, the mean flap thickness was 131.7 μm centrally, 155.5 μm superiorly, 146.7 μm inferiorly, 143.7 μm temporally, and 160.5 μm nasally. There was a statistically significant difference between flap thickness centrally and in the other areas (P>.05). With the Amadeus microkeratome, the mean flap thickness was 140.0 mum centrally, 152.5 superiorly, 128.5 mum inferiorly, 145.0 mum temporally, and 147.0 mum nasally. Statistically significant differences (P>.05) were found in the 4 sectors of the flap. With vectorial analysis, there was no statistically significant difference between superonasal and superotemporal hinge placement in the cardinal and oblique components but there was a statistically significant difference in the axis change with both placements (P>.05). Conclusions: The LSX One microkeratome was the most predictable. A significant difference was noted in all sectors except superiorly with the M2 and in all sectors with the Amadeus. No differences between nasal and superior hinge placement were found with the M2. Topographic Zernike analysis demonstrated a difference in the orientation of the induced coma as a function of hinge position.