Staging of keratoconus indices regarding tomography, topography, and biomechanical measurements

Goebels, Susanne; Eppig, Timo; Wagenpfeil, Stefan; Cayless, Alan; Seitz, Berthold and Langenbucher, Achim (2015). Staging of keratoconus indices regarding tomography, topography, and biomechanical measurements. American Journal of Ophthalmology, 159(4) pp. 733–738.

DOI: https://doi.org/10.1016/j.ajo.2015.01.014

URL: http://www.ajo.com/article/S0002-9394%2815%2900043...

Abstract

Purpose
To derive limits of metric keratoconus indices for classification into keratoconus stages.

Design
Validity and reliability analysis of diagnostic tools.

Methods
A total of 126 patients from the keratoconus center of Homburg/Saar were evaluated with respect to Amsler criteria, using Pentacam (Keratoconus Index [KI], Topographic Keratoconus Classification [TKC]), Topographic Modeling System (Smolek/Klyce, Klyce/Maeda), and Ocular Response Analyzer (Keratoconus Match Probability [KMP], Keratoconus Match Index [KMI]). Mean value, standard deviation, 90% confidence interval, and the Youden J index for definition of the thresholds were evaluated.

Results
For separation of keratoconus stages 0/1/2/3/4 we derived the following optimum thresholds: for KI 1.05/1.15/1.31/1.49 and for KMI 0.77/0.32/-0.08/-0.3. For Smolek/Klyce and Klyce/Maeda high standard deviations and overlapping confidence intervals were found; therefore no discrete thresholds could be defined. Nevertheless, for them we still found a good sensitivity and specificity in discriminating between healthy (stage 0) and keratoconus (stages 2–4) eyes in comparison with the other indices.

Conclusions
We derived thresholds for the metric keratoconus indices KI and KMI, which allow classification of keratoconus stages. These now need to be validated in clinical use. Smolek/Klyce and Klyce/Maeda were not sufficiently sensitive to allow classification into individual stages, but these indices did show a good specificity and sensitivity in discriminating between keratoconus and healthy eyes.

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