Mohammad Naderan1, Mohammad Taher Rajabi2, Parviz Zarrinbakhsh3. 1. 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. 2. Eye Research Center, Farabi Eye Hospital, Tehran University of Medical Sciences, Tehran, Iran. 3. Zarrinbakhsh Eye Clinic, Tehran, Iran.
Abstract
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.
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.
Authors: Sepehr Feizi; Siamak Delfazayebaher; Mohammad Ali Javadi; Farid Karimian; Vahid Ownagh; Fatemeh Sadeghpour Journal: J Ophthalmic Vis Res Date: 2018 Apr-Jun