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Lorant Dienes, Kinga Kranitz, Andrea Gyenes, Eva Juhasz, Janos Nemeth, Illes Kovacs, Zsolt Z Nagy, ; Between-eye Asymmetry Detected by Scheimpflug Imaging in Subjects With Normal Corneas and Keratoconus. Invest. Ophthalmol. Vis. Sci. 2014;55(13):4205.
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To evaluate the diagnostic accuracy of measuring between-eye asymmetry with regard to pachymetry and corneal elevation in the prediction of keratoconus.
This study included 115 patients: 68 subjects with bilateral normal corneas (NC) and 47 with bilateral keratoconus (KC) including 10 forme fruste corneas. Central corneal thickness (CCT), pachymetry at the thinnest point (ThCT), posterior elevation at the thinnest point of the cornea (PE) was measured in both eyes using Scheimpflug imaging. Between-eye asymmetry was determined by subtracting the lower value from the higher value for each variable. Covariate adjustment for area under the receiver operating characteristic curve (AUROC) was used to determine predictive accuracy of different variables to identify keratoconic corneas.
In normal subjects, the mean between-eye assymetry in CCT, ThCT and PE were 5.59±4.90 µm, 6.57±5.30 µm and 3.13±3.71 µm, respectively. In keratoconus patients, the mean asymmetry in CCT, ThCT and PE were 30.13±35.80 µm, 39.70±36.42 µm and 35.40±37.31 µm. In normal eyes, the mean between-eye asymmetry were significantly lower compared with the keratoconic eyes (p<0.001 for CCT, ThCT and PE). There was significant correlation between ThCT and asymmetry of ThCT (KC: r=-0.40, p=0.003), between CCT and asymmetry of CCT (KC: r=-0.72, p=0.002) and between PE and asymmetry of PE (KC: r=0.82, p<0.001) in the keratoconus group, but not in the control group (p>0.05 for all of the variables). After adjustment for these correlations, between-eye asymmetry of CCT, ThCT and PE showed high accuracy to predict keratoconus with an AUROC value of 0.99 for ThCT, 0.94 for CCT and 0.96 for PE.
There is a greater between-eye asymmetry in pachymetry and posterior corneal elevation values in keratoconic patients than in subjects with normal corneas. After adjustment for the significant effect of keratoconus progression measured by increase in posterior elevation or by decrease in pachymetry on between-eye asymmetry keratoconic eyes can be identify with high accuracy.This method may help to identify corneas with risk of developing corneal ectasia with simple pachymetry measurements.
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