Abstract
Purpose: :
The purpose of this analysis was to investigate the ocular higher order aberration (HOA) profile for myopes and hyperopes before and after CustomCornea® LASIK (Alcon Laboratories, Inc). Individual Zernike coefficients up to the 4th order were analyzed in order to examine their directionality.
Methods: :
CustomCornea® LASIK was performed on 156 myopic eyes (79 patients) and 51 hyperopic eyes (27 patients). Preoperative myopic and hyperopic wavefront sphere were –2.87 ± 1.30D and +2.91 ± 1.52D with mean cylinder –0.74 ± 0.62D and –1.39 ± 0.93D, respectively. Wave aberrations were described as Zernike polynomial expansions over a 5mm pupil. Using OSA standards, each HO Zernike term represents the following: Z(3,1), Z(3,–1) = horizontal, vertical coma; Z(3,3), Z(3,–3) = horizontal, oblique trefoil; Z(4,0) = spherical aberration (SA); Z(4,2), Z(4,–2) = with/against the rule and oblique secondary astigmatism; and Z(4,4), Z(4,–4) = horizontal, oblique quatrefoil. Changes in magnitude were either positive or negative. Repeated measures ANOVA and t–tests were used and p<0.05 was considered statistically significant.
Results: :
Preoperatively, HOAs were not statistically different between the myopic and hyperopic groups with the exception of Z(4,0) and Z(4,4), which were greater and more positive for the hyperopes (p<0.01). At the 6–month visit the greatest change in magnitude occurred for Z(3,–1) and Z(4,0), both of which changed in a positive direction for myopes and in a negative direction for hyperopes (p<0.05). In addition, Z(3,3) was found to be greater and more negative; Z(3,–3) greater and more positive for the hyperopic group compared to the myopic group after surgery (all p<0.01).
Conclusions: :
Preoperatively, spherical aberration (SA) and horizontal quatrefoil were greater and more positive for the hyperopic group. Postoperatively, the most notable changes were vertical coma and SA, which changed in a positive direction for myopes and a negative direction for hyperopes. Although the difference in SA between groups is not entirely unexpected, the difference in vertical coma has not been previously reported. As the overall directionality of change is lost when calculating rms error, individual Zernike terms are valuable.
Keywords: refractive surgery: LASIK • refractive surgery: optical quality