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Subject Area

Ophthalmology

Article Type

Original Study

Abstract

Objective The aim was to evaluate the magnitudes and axis orientation of anterior corneal astigmatism (ACA) and posterior corneal astigmatism (PCA) and the correlation between ACA and PCA in the different stages of keratoconus (KC). Background PCA is an essential factor to be considered for accurate measurement of intraocular lens (IOL) power used in the treatment of cataract with KC. Patients and methods A retrospective case series study was conducted between August 2017 and July 2018 on a sample of 94 eyes with KC. Participants were divided into four subgroups according to Amsler–Krumeich classification. Pentacam was used to measure the magnitude and axis orientation of ACA and PCA. A correlation between ACA and PCA in the different stages of KC was also done. Results The means of anterior and PCA were 3.5 ± 3.02 diopters (D) and 0.72 ± 0.53 D, respectively. With-the-rule astigmatism was the dominant type of astigmatism orientation at both anterior (80.9%) and posterior (87.2%) corneal surfaces, some were oblique, and there were no cases with against-the-rule astigmatism orientation. There was a strong correlation (P < 0.001) between ACA and PCA in the different stages of KC, and the correlation was lower in eyes with grade 2 (P = 0.002) and grade 3 (P = 0.01) KC. Conclusion The prevalence rates of with-the-rule orientation of the ACA and PCA were higher than those for oblique orientation, and there were no cases with against-the-rule astigmatism orientation. The corneal astigmatism values at the two surfaces were significantly associated with the severity of KC, and the ACA and PCA values were strongly correlated.

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