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Characteristics of posterior corneal astigmatism in different stages of keratoconus

Poster Details

First Author: M.Khorrami-Nejad IRAN

Co Author(s):    F. Aslani   M. Khodaparast   F. Askarizadeh              

Abstract Details


To evaluate the magnitudes, axis orientation, ratio and correlation of anterior corneal astigmatism(ACA) and posterior corneal astigmatis(PCA) in different stage of keratoconus(KCN).


Eye Research Center, Farabi Eye Hospital, Tehran University of Medical Sciences, Tehran, Iran


This retrospective case series study comprised 161 eyes of 161 KCN patients (104 men and 57 women; mean age �Â�± standard deviation,22.35 �Â�± 6.10 years) that was divided into 4 subgroups according to the Amsler-Krumeich classification. Scheimpflug imaging system (OCULUS Optikgerate GmbH, Wetzlar, Germany( was used to measure the magnitude and the axis orientation of ACA and PCA. The posterior�â�€�“anterior corneal astigmatism ratio was also calculated.


The mean magnitudes of anterior, posterior, and total central corneal astigmatism were 4.08 diopters (D), 0.86 D, and 3.50 D, respectively. With-the-rule, against-the-rule, and oblique astigmatism of the posterior corneal surface was found in 61 eyes (37.9%), 67eyes (41.6%), and 33 eyes (20.5%), respectively, whereas the corresponding astigmatism of the anterior corneal surface was found in 55 eyes (32.4%), 56 eyes (34.8%), and 50 eyes (31.1%), respectively. A strong correlation (P�â�‰�¤0.001, r=0.839) was found between ACA and PCA in the different stage of KCN; the correlation was weaker in grades 3(P�â�‰�¤0.001, r=0.711) and 4(P�â�‰�¤0.001, r=0.717) KCN cases.


Cornea astigmatism in anterior surface more affected than posterior surface by an increase in the KCN severity and in opposite PCA more affected than ACA in early stage of KCN.

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