title: Distribution of Anterior and Posterior Corneal Astigmatism in Eyes With Keratoconus.
abstract: 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.
  
  
  
  Retrospective age- and sex-matched case-control study.
  
  
  
  Using the Pentacam images, the aforementioned parameters were compared between 1273 patients with KC and 1035 normal participants.
  
  
  
  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.
  
  
  
  Our findings can help clinicians in the diagnosis of KC and lens manufacturers in designing suitable contact or intraocular lenses.
authors.affiliation: Eye Research Center, Farabi Eye Hospital, Tehran University of Medical Sciences, Tehran, Iran; Ophthalmic Research Center, Shahid Beheshti University of Medical Sciences, Tehran, Iran. Electronic address: Moh@Naderan.com.
authors.forename: Mohammad
authors.initials: M
authors.lastname: Naderan
authors.affiliation: Eye Research Center, Farabi Eye Hospital, Tehran University of Medical Sciences, Tehran, Iran.
authors.forename: Mohammad Taher
authors.initials: MT
authors.lastname: Rajabi
authors.affiliation: Zarrinbakhsh Eye Clinic, Tehran, Iran.
authors.forename: Parviz
authors.initials: P
authors.lastname: Zarrinbakhsh
mesh_terms: D000328:Adult; D001251:Astigmatism / Q000175:diagnosis*; D016022:Case-Control Studies; D003941:Diagnostic Techniques, Ophthalmological; D004728:Endothelium, Corneal / Q000473:pathology*; D019573:Epithelium, Corneal / Q000473:pathology*; D005189:False Positive Reactions; D005260:Female; D006801:Humans; D007640:Keratoconus / Q000175:diagnosis*; D008297:Male; D010781:Photography / Q000295:instrumentation*; D011237:Predictive Value of Tests; D012372:ROC Curve; D015203:Reproducibility of Results; D012189:Retrospective Studies; D012680:Sensitivity and Specificity; D055815:Young Adult