Cornea

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Cornea:
doi: 10.1097/ICO.0B013E31823D1EE0
Clinical Science

Correlation of Corneal Elevation With Severity of Keratoconus by Means of Anterior and Posterior Topographic Analysis

Ishii, Rie MD*; Kamiya, Kazutaka MD, PhD*; Igarashi, Akihito MD, PhD*; Shimizu, Kimiya MD, PhD*; Utsumi, Yoshikazu MD, PhD*†; Kumanomido, Takashi MD*‡

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Abstract

Purpose: To investigate the severity of keratoconus in terms of corneal elevation differences with 2 different reference surfaces using topographic analysis.

Methods: Eighty-six eyes of 50 patients with keratoconus of various clinical stages (61 male and 25 female eyes) with mean age of 37.3 ± 11.6 years were evaluated. Anterior and posterior corneal elevations were measured using topographic analysis (using a rotating Scheimpflug camera), and the imaging data were analyzed to estimate elevation differences as differential values from conventional best-fit-sphere and enhanced best-fit-sphere (exclusion of a 4-mm-diameter area from the most thinned cornea). The data correlated with the keratoconus severity index and Amsler–Krumeich classification of keratoconus.

Results: There was a significant positive correlation between elevation differences and keratoconus severity index in both anterior and posterior surfaces (Pearson correlation coefficient, r = 0.66; P < 0.001; r = 0.74; P < 0.001). Cases of larger elevation differences in the anterior and posterior corneal surfaces were staged higher in Amsler–Krumeich classification (1-way analysis of variance, P = 0.040; P < 0.001). Cases of lower staging in the Amsler–Krumeich classification had a larger area under the receiver operating characteristic curve in the posterior elevation differences than in the anterior elevation differences, suggesting a greater diagnostic value of the posterior elevation measurement.

Conclusions: Anterior and posterior corneal surface height data obtained by elevation-based tomography provide useful information in improving keratoconus diagnostic accuracy and in grading the severity of keratoconus.

© 2012 Lippincott Williams & Wilkins, Inc.

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