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Characteristics of Posterior Corneal Astigmatism in Different Stages of Keratoconus Publisher



Aslani F1 ; Khorraminejad M1, 2 ; Amiri MA1 ; Hashemian H2 ; Askarizadeh F1 ; Khosravi B1
Authors
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Authors Affiliations
  1. 1. Department of Optometry, Faculty of Rehabilitation, Shahid Beheshti University of Medical Sciences, Damavand St., Tehran, 16169, Iran
  2. 2. Eye Research Center, Farabi Eye Hospital, Tehran University of Medical Sciences, Tehran, Iran

Source: Journal of Ophthalmic and Vision Research Published:2018


Abstract

Purpose: To evaluate the magnitudes and axis orientation of anterior corneal astigmatism (ACA) and posterior corneal astigmatism (PCA), the ratio of ACA to PCA, and the correlation between ACA and PCA in the different stages of keratoconus (KCN). Methods: This retrospective case series comprised 161 eyes of 161 patients with KCN (104 men, 57 women; mean age, 22.35 ± 6.10 years). The participants were divided into four subgroups according to the Amsler-Krumeich classification. A Scheimpflug imaging system was used to measure the magnitude andaxis orientation of ACA and PCA. The posterior-anterior corneal astigmatism ratio was also calculated. The results were compared among different subgroups. Results: The average amounts of anterior, posterior, and total corneal astigmatism were 4.08 ± 2.21 diopters (D), 0.86 ± 0.46 D, and 3.50 ± 1.94 D, respectively. With-the-rule, against-the-rule, and oblique astigmatisms of the posterior surface of the cornea were found in 61 eyes (37.9%), 67 eyes (41.6%), and 33 eyes (20.5%), respectively; corresponding figures in the anterior corneal surface were 55 eyes (32.4%), 56 eyes (34.8%), and 50 eyes (31.1%), respectively. A strong correlation (P = 0.001, r = 0.839) was found between ACA and PCA in the different stages of KCN; the correlation was weaker in eyes with grade 3 (P = 0.001, r = 0.711) and grade 4 (P = 0.001, r = 0.717) KCN. The maximum posterior-anterior corneal astigmatism ratio (PCA/ACA, 0.246) was found in patients with stage 1 KCN. Conclusion: Corneal astigmatism in anterior surface was more affected than posterior surface by increasing in the KCN severity, although PCA was more affected than ACA in an early stage of KCN. © 2018 Journal of Ophthalmic and Vision Research | Published by Wolters Kluwer - Medknow.