Comparison of higher-order aberration induction between manual microkeratome and femtosecond laser flap creation.

PURPOSE: To compare the mean change in aberrations produced by a mechanical microkeratome and femtosecond laser.

METHODS: This was a retrospective study of 62 consecutive near emmetropic eyes that underwent LASIK and satisfied the following criteria: negligible laser ablation (for spherical equivalent of 0.00 to +0.50 diopters and maximum meridian of +0.50 diopters), and preoperative and at least 3 months postoperative Placido-based corneal aberrometry (ATLAS; Carl Zeiss Meditec, Jena, Germany). Eyes were divided into two groups according to the method used for flap creation: mechanical microkeratome (Hansatome zero-compression microkeratome; Bausch & Lomb, Rochester, NY [mechanical microkeratome group]) or femtosecond laser (VisuMax; Carl Zeiss Meditec, Jena, Germany [femtosecond laser group]). The root mean square total and individual higher-order aberrations were compared between the two groups.

RESULTS: Corneas with mechanical flaps, on average, possessed statistically significantly higher trefoil and horizontal coma (P < .001). There was no change in higher-order aberrations, except for spherical aberration in the femtosecond laser group. Average change in coma did not correlate with hinge position. Both groups showed statistically significant changes in spherical aberration (P < .001), although this was most likely due to the small hyperopic ablation performed.

CONCLUSIONS: There was greater induction of specific aberrations with the microkeratome than the femtosecond laser. Hinge position did not appear to influence the induction of coma directly, contrary to previously published reports. The difference in aberrations induction between the two groups might be due to the differences in flap thickness profiles.