Epithelial Thickness Analysis Using Anterior Segment Optical Coherence Tomography In Keratoconus Patients With Very Asymmetric Ectasia

Anterior segment optical coherence tomography (AS-OCT) enables fast epithelial thickness measurements, which could be helpful in detecting corneal ectasia. In keratoconus, epithelial thinning is observed in the cone area, with a thickened epithelium around it, which results in high localized epithelial thickness differences. The aim of the study was to develop a method for quantifying the epithelial thickness differences in keratoconus, and to test it on Scheimpflug-tomographically normal fellow eyes in keratoconus patients with very asymmetric ectasia (VAE).

International Vision Correction Research Centre (IVCRC), Department of Ophthalmology, University of Heidelberg, Heidelberg, Germany.

Twenty-one patients with tomographically-significant ectasia in one eye and a tomographically-normal fellow eye (VAE) could by identified by Pentacam (Oculus, Wetzlar, Germany). Twenty-one healthy subjects served as a control group. The epithelial thickness data were obtained using AS-OCT ANTERION (Heidelberg Engineering, Heidelberg, Germany). Mean absolute epithelial thickness differences around each of the 25 zones of the epithelial thickness map were calculated and the difference maps were created. Then, we compared the averaged data from the temporal-inferior quadrant between VAE patients and healthy controls using Mann-Whitney-U-test with Bonferroni correction. The p-value of <0.05 was considered statistically significant. 

Epithelial thickness difference maps showed the tendency towards higher values in the temporal-inferior quadrant in tomographically-significant keratoconus eyes. Compared to healthy controls, the mean (±standard deviation) epithelial thickness difference in the temporal-inferior quadrant was higher not only in tomographically-significant keratoconus, but also in tomographically-normal fellow eyes (1.0±0.4 µm vs. 4.6±2.0 µm and 1.3±0.4 µm, p<0.05). The cut-off value of 1.8 µm had both the sensitivity and specificity of 95.2% in differentiating tomographically-significant keratoconus from healthy eyes, while 9.5% (n=2) of the tomographically-normal keratoconus fellow eyes also had elevated (>1.8 µm) epithelial thickness difference values.

Epithelial thickness difference mapping could detect pathological epithelial thickness changes in 95% of eyes with tomographically-significant keratoconus. In comparison to healthy eyes, the tomographically-normal keratoconus fellow eyes had statistically significantly higher epithelial thickness difference values, indicating that this parameter could potentially be useful for early ectasia screening.