Correlation between Corneal Topographic Indices and Higher-Order Aberrations in Keratoconus

PURPOSE: To compare corneal higher-order aberrations (HOAs) between normal and keratoconic eyes, and to investigate the association between elevation-based corneal topographic indices and corneal wavefront data in the latter group. METHODS: In this cross-sectional comparative study, 77 normal right eyes of 77 control subjects and 66 eyes of 36 keratoconic patients were included. In each eye, elevation- based corneal topographic indices including mean keratometry readings, best-fit sphere, maximum elevation, and 3-mm and 5-mm zone irregularity indices were measured using Orbscan II. The Galilei Scheimpflug analyzer was used to measure HOAs of the corneal surface. The independent student t-test was used to compare HOAs between the study groups. Spearman correlation was used to investigate possible associations between Orbscan and Galilei data in the keratoconus group. RESULTS: All Zernike coefficients up to the 4th order except for horizontal trefoil, and vertical and horizontal tetrafoil were significantly greater in the keratoconus group than normal eyes (P<0.05). Root mean square (RMS) of HOAs up to the 6th order and total HOAs were significantly higher in the keratoconus group (P<0.05). In the keratoconus group, the strongest association was observed between vertical coma (r=-0.71, P<0.01) and total RMS of HOAs (r=0.94, P<0.01) with irregularity in the 3-mm zone. Spherical and vertical coma aberrations were significantly correlated with mean keratometry (P<0.05 for both comparisons). CONCLUSION: Centrally located corneal HOAs are significantly greater in keratoconic eyes than normal controls. Anterior and inferior displacement of the cornea causes the majority of higher-order aberrations observed in keratoconus.