AIM: To compare the regularity and accuracy of laser in situ keratomileusis (LASIK) flaps created by the Ziemer FEMTO LDV “Classic” (Ziemer “Classic”) and Ziemer FEMTO LDV Crystal Line femtosecond laser (Ziemer Crystal Line).METHODS:Fourier-domain optical coherence tomography (RTVue OCT) was used tomeasure the morphology of 200 LASIK flaps of 100 consecutive patients created with the Ziemer Classic (100 flaps) or the Ziemer Crystal Line (100 flaps) at one week postoperatively. Flap thickness was evaluated at 36 specified measurement points on each flap. For all procedures with both lasers, the nominal flap thickness was 110μm.RESULTS:The mean flap thickness of the Ziemer Crystal Line group(102.49±2.68μm) was thinner than that of the Ziemer Classic group (107.65±5.09μm) (P<0.01). Average thickness of all flaps was uniform within 4μm at all measurement points. The flaps in the Ziemer Crystal Line group were more regular than those in the Ziemer Classic group when measured from the center to the periphery. The maximum deviation from the nominal 110μm of 36 measurements was 8μm in the Ziemer Classic group, while in the Ziemer Crystal Line group it was 9μm. Within the 3 600 measurements on the 100 eyes, differences greater than 20μm were observed 0.14% in the Ziemer Classic group, and 0.04% in the Ziemer Crystal Line group.CONCLUSION:The flaps created with the Ziemer FEMTO LDV Crystal Linefemtosecond laser are more uniform and thinner than those created by the Ziemer FEMTO LDV Classic femtosecond laser.