Influence of pupil and optical zone diameter on higher-order aberrations after wavefront-guided myopic LASIK

PURPOSE: To investigate the influence of pupil and optical zone (OZ) diameter on higher-order aberrations (HOAs) after myopic wavefront-guided laser in situ keratomileusis (LASIK). METHODS: Twenty-seven myopic eyes of 19 patients were included. The mean preoperative spherical equivalent was -6.86 diopters (D) +/- 1.24 (SD) (range -4.25 to -9.5 D); the mean planned OZ diameter was 6.26 +/- 0.45 mm (range 5.7 to 7.1 mm). All patients had uneventful wavefront-guided LASIK (Zyoptix version 3.1, Bausch & Lomb) and an uncomplicated follow-up of 12 months. Wavefront measurements were performed with a Hartmann-Shack sensor in maximum mydriasis preoperatively and 12 months after LASIK. Wavefront errors were computed for pupil diameters (PDs) of 3.0, 3.5, 4.0, 5.0, 6.0, and 7.0 mm for the individual OZ diameter and for the individual mydriatic PD (7.93 +/- 0.46 mm). The impact of the relationship between pupil diameter and OZ diameter (fractional clearance [FC]) on HOA was described and quantified using curvilinear regression with a 4th-order polynomial fit. RESULTS: There was a reproducible relationship between FC and the amount of induced HOA. The change in HOA root mean square and primary spherical aberration (Z(4)0) was significantly correlated with FC. If the OZ was 16.5% larger than the pupil (FC = 1.17), only half the amount of HOA was expected to be induced than if the OZ equaled the pupil. In contrast, an OZ that was 9% smaller than the pupil (FC = 0.91) resulted in an HOA induction 50% higher than at FC = 1. CONCLUSION: The OZ zone to pupil ratio (fractional clearance) had a significant impact on HOA induction after wavefront-guided LASIK.