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Ciara Bergin, Francois Majo, Kattayoon Hashemi, Ivo Guber; Relationship between repeatability in corneal topography parameters and increased disease severity in keratoconic eyes. Invest. Ophthalmol. Vis. Sci. 2016;57(12):2899. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
Good repeatability of topographic measurements has been demonstrated in normal eyes but a clinically significant reduction in repeatability has been recently identified in keratoconic eyes. The aim of this study was to evaluate the relationship between repeatability and disease severity in keratoconic eyes measured by the Pentacam HR® device and to identify the best performing parameters in each disease stage.
This is an intra-instrument repeatability assessment study. Two hundred and forty eight keratoconic eyes of 197 patients were identified. All available images were exported automatically from the Pentacam HR device. Two good quality images taken on the same day within the same sitting were extracted and the repeatability between these two measures was assessed. The limits of repeatability (r) at each stage of keratoconus (KCN )to determine those limits significantly different than r in healthy eyes. The r were also compared with the length of the respective range to determine the relative utilty (RU) of each parameter at each stage of KCN. High RU values indicate a parameters best positioned to detect disease progression.
Mean age was 35.3 years, average maximal corneal curvature (Kmax) was 55.3D, mean minimum pachymetry was 458mm. Mean r of K-max was 0.7D, 1.3D, 1.8D and 2.4D for topographic keratoconus classification (TKC) grade 1, 2, 3 and 4 respectively. A highly significant relationship between K-max and repeatability was observed, p<0.001, significantly increasing with each stage of KCN. Astigmatism and Belin Ambrosia score had high RU values in new cases of KCN (TKC1), while the anterior corneal curvature parameters are best placed to distinguish disease progression (TKC 2-4).
The results of the present study suggest that progression will be more difficult to detect accurately using topographic measures in patients with high corneal curvature and/or more advanced KCN. The RU gives a systematic approach to detect parameters best positioned to detect change at each stage of disease. In this study those parameters with high RU values were isolated for each stage of KCN and appropriate limits of repeatability for <span style="line-height:20.7999992370605px">each parameter in </span>each stage of KCN were provided. This information should help the clinician more accurately assess KCN progression with topography images.
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.
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