[The study of corneal epithelial change in keratoconic eyes with Fourier-domain optical coherence tomographic pachymetry].

OBJECTIVE: To compare the corneal epithelial thickness profile in keratoconic and normal eyes with advanced Fourier-domain optical coherence tomography (OCT) and to evaluate the diagnostic efficiency of pachymetry parameters.

METHODS: Cross-sectional observational study. Twenty-five consecutive keratoconus patients (34 eyes) and 41 normal volunteers (41 eyes) in Eye & ENT Hospital of Fudan University between June 1 and July 31, 2013 were enrolled.Observations of corneal epithelial thickness and corneal thickness profiles were taken from all subjects. The epithelial pachymetry parameters were superior, inferior, inferior-superior (I-S), minimum (Min), maximum (Max), Min-Max, and central. The corneal pachymetry parameters were inferotemporal-superonasal (IT-SN), I-S, Min, Min-median, Min-Max, and central.Statistical analysis methods included Chi-square test, independent two-sample t-test, and Wilcoxon rank sum test. The diagnostic efficiency of all parameters were analyzed by receiver operating characteristic (ROC) curves and Youden index.

RESULTS: The inferior, I-S, Min, Min-Max, and central epithelial thickness averages were (50.5 ± 4.8) µm, (-2.7 ± 7.5) µm, (35.9 ± 10.7) µm, (-33.6 ± 18.9) µm, and (50.1 ± 6.8) µm in keratoconic eyes.In normal eyes, they were (54.8 ± 2.5) µm, (0.9 ± 1.3) µm, (51.4 ± 2.6) µm, (-5.7 ± 1.8) µm, and (54.7 ± 2.2) µm. Among the epithelial pachymetry parameters, Min-Max and Min showed high diagnostic efficiency for keratoconus (AUC = 0.967, 0.968; Youden index = 0.882, 0.829); inferior, I-S, and central parameters showed moderate efficiency (AUC = 0.794, 0.728, 0.715; Youden index = 0.461, 0.564, 0.565). The IT-SN, I-S, Min, Min-median, Min-Max, and central corneal thickness averages were (-82.8 ± 65.2) µm, (-72.5 ± 55.6) µm, (401.2 ± 83.8) µm, (-83.4 ± 48.2) µm, (-169.7 ± 99.4) µm, and (453.4 ± 58.6) µm in keratoconic eyes.In normal eyes, these parameters were respectively (-23.7 ± 18.5) µm, (-20.5 ± 19.8) µm, (525.4 ± 28.1) µm, (-23.1 ± 4.8) µm, (-59.2 ± 23.3) µm, and (533.4 ± 28.8) µm. Min, Min-median, and Min-Max had preferable diagnostic efficiency (AUC = 0.952, 0.938, 0.924; Youden index = 0.784, 0.829, 0.721); central, IT-SN, and I-S parameters showed moderate efficiency (AUC = 0.891, 0.877, 0.862; Youden index = 0.643, 0.707, 0.580).

CONCLUSIONS: In observation with Fourier-domain OCT, keratoconus was characterized by central and inferior epithelial thinning, increased epithelial thickness variation, central cornea thinning, increase in asymmetry, and gaps between corneal IT-SN and I-S thickness.Fourier-domain OCT was confirmed to have high speed, high resolution, and noninvasion. The pachymetry parameters showed specific strengths in diagnosis of keratoconus, especially epithelial pachymetry parameters of Min and Min-Max, and corneal pachymetry parameters of Min, Min-median and Min-Max.