Comparison of corneal flaps created by three femtosecond lasers for laser in situ keratomileusis

PurposeTo evaluate the predictability and uniformity of femtosecond laser-assisted in situ keratomileusis flap created by 3 femtosecond lasers.Methods：In this prospective study, 196 corneal flaps were performed by LDV Z8 (66 eyes), LDV Z2 (70 eyes), VisuMax (60 eyes) laser. The expected flap thickness was 100 μm. Flap thickness was measured one week postoperatively at 28 points using RTVue Fourier-domain optical coherence tomography (OCT).The side-cut angle was measured at three peripheral positions.ResultsThe LDV Z8 had a significantly thicker mean central flap thickness (107.0 ± 5.0 μm) and mean flap thickness (110.5 ± 4.0 μm) compared to both the LDV Z2 (mean central 103.1 ± 4.2 μm (P ＜ 0.001), mean 107.5 ± 4.0 μm (P ＜ 0.001)) and the VisuMax (mean central 105.1 ± 5.4 μm (P ＜ 0.027), mean 108.3 ± 3.9 μm(P ＜ 0.002)). The mean overshoot of flap thickness between the actual and planned values was statistically significant (all groups, <i>P</i> < 0.001). The corneal flap thicknesses of the 0-, 45-, 90- and 135-degree meridians showed great uniformity in all groups. The center-peripheral corneal thickness difference in the LDV Z2 (6.1 ± 3.3 μm) was larger compared to the differences in the LDV Z8 (4.0 ± 3.9 μm) (<i>P</i> = 0.003) and the VisuMax (3.4 ± 5.1 μm) (<i>P</i> = 0.002). The mean side-cut angles for the VisuMax, LDV Z8, and LDV Z2 were 62.4 ± 4.5 degrees, 92.3 ± 14.4 degrees, and 147.6 ± 6.7 degrees, respectively.ConclusionThe corneal flaps generated by three femtosecond lasers exhibit good morphology. The thickness of the flaps in all groups was close to but slightly thicker than the target thickness.