Factors affecting the change in lower-order and higher-order aberrations after wavefront-guided laser in situ keratomileusis for myopia with the Zyoptix 3.1 system.

PURPOSE

To identify factors that affect the change in lower- and higher-order wavefront aberrations after myopic wavefront-guided laser in situ keratomileusis (wg-LASIK).

SETTING

Department of Ophthalmology, Johann Wolfgang Goethe-University, Frankfurt am Main, Germany.

METHODS

Sixty myopic eyes of 32 patients were treated with wg-LASIK (Zyoptix version 3.1, Bausch & Lomb) and had an uneventful follow-up of 12 months. Wavefront errors were measured preoperatively and 12 months after LASIK and were computed for pupil diameters (PDs) of 3.5 mm and 6.0 mm. Multiple stepwise regression analysis was performed to assess the influence of patient age, spherical equivalent (SE), sphere, cylinder, optical zone (OZ) diameter, and the preoperative individual Zernike coefficients on lower- and higher-order aberration (HOA) change.

RESULTS

The mean preoperative SE was -5.59 diopters (D) +/- 2.20 (SD) (range -1.00 to -9.50 D); the mean OZ diameter was 6.70 +/- 0.68 mm (range 5.6 to 8.1 mm). Reduction in almost all Zernike coefficients was influenced significantly by the preoperative amount of the individual coefficient. The effect varied among the coefficients and was lower with the 6.0 mm PD. With the 3.5 mm PD, age, SE, sphere, cylinder, and OZ diameter did not have a significant effect on individual Zernike coefficients. With the 6.0 mm PD, SE and OZ diameter had a significant effect on the induction of Z4(0); the OZ diameter also had an effect on the induction of coma root mean square.

CONCLUSIONS

Three groups of factors influenced the change in HOAs: The negative correlation with the magnitude of preoperative HOA values reflected the effect of the wavefront-guided algorithm. The SE and OZ diameter affected the inadvertent induction of spherical aberrations. Randomly acting effects such as decentration or flap creation, which were not included in the model, affected the induction of HOAs, particularly coma-like terms.