Distribution of Anterior and Posterior Corneal Astigmatism in Eyes With Keratoconus.

PURPOSE: To investigate the magnitude, with-the-rule (WTR) or against-the-rule (ATR) orientation, and vector components (Jackson astigmatic vectors [J0 and J45] and blurring strength) of the anterior and posterior corneal astigmatism (ACA and PCA) in patients with keratoconus (KC) in a retrospective study, and to try to find suitable cutoff points for ACA and PCA in an attempt to discriminate KC from normal corneas.

DESIGN

Retrospective age- and sex-matched case-control study.

METHODS

Using the Pentacam images, the aforementioned parameters were compared between 1273 patients with KC and 1035 normal participants.

RESULTS

The mean magnitude of the ACA and PCA was 4.49 ± 2.16 diopter (D) and 0.90 ± 0.43 D, respectively. The dominant astigmatism orientation of the ACA was ATR in KC patients and WTR in normal participants (P < .001), while for the PCA it was WTR in KC patients and ATR in normal participants (P < .001). There was a significant agreement between the axis orientations of ACA and PCA in KC patients (ĸ = 0.077, P < .001), but not in the normal group (P = .626). ACA and PCA magnitude, M, J0, J45, and blur significantly increased by increasing KC severity. There was a trend for increasing anterior ATR and posterior WTR, and decreasing oblique astigmatism on both corneal surfaces by increasing the KC severity according to the Amsler-Krumeich classification. A cutoff value of 1.8 D for ACA had 90.2% sensitivity and specificity, and that of 0.4 D for PCA had 89.5% sensitivity and 85.0% specificity for discriminating KC from normal corneas.

CONCLUSION

Our findings can help clinicians in the diagnosis of KC and lens manufacturers in designing suitable contact or intraocular lenses.