The role of the corneal epithelial thickness parameters measured with ultra-high resolution optical coherence tomography in the diagnosis of keratoconus

Objective To investigate the role of the corneal epithelial thickness (EP) parameters measured with ultra-high resolution optical coherence tomography (UHR-OCT) in the diagnosis of keratoconus. Methods In this cross-sectional observational study, 20 patients with keratoconus (20 eyes) and 20 normal volunteers (20 eyes) were recruited in the study. Corneal epithelial thickness profiles were taken from all subjects. The parameters included mean thickness (MEAN), minimum thickness (MIN), epithelial ectasia index (EEI), defined as epithelial thickness minimum thickness of the inferior half of the cornea divided by corneal epithelial thickness average thickness of the superior half of the cornea multiplied by 100, maximal epithelial ectasia index (EEI-MAX), defined as corneal epithelial thickness minimum thickness of the inferior half of the cornea divided by corneal epithelial thickness maximum thickness of the superior half of the cornea multiplied by 100, epthetlium standard variation (ESV). Statistical analysis methods included independent samplest-test and receiver operating characteristic (ROC) curves. Results In normal eyes, the MEAN, MIN, EEI, EEI-MAX, ESV were 52.52±2.64 μm, 50.05±3.38 μm, 97.93±4.59, 91.60±4.54, 2.94±0.56. In keratoconic eyes, they were 51.33±3.78 μm, 38.86±5.45 μm, 77.13±10.59, 67.45±12.64, 7.02±2.55. Among the epithelial pachymetry parameters, ESV showed highest diagnostic efficiency and diagnostic value for keratoconus, the area under the ROC curve (AUC) was 1.000 and the positive predictive value was 1.000. MIN, EEI, EEI-MAX also have high diagnostic efficiency and diagnostic value, the AUC were 0.955, 0.945, 0.950, and the positive predictive value were 0.900, 0.900, 0.950. Conclusion keratoconus is characterized by central and inferior epithelial thinning surrounded by thickened epithelium. The epithelial pachymetry parameters show excellent accuracy, sensitivity, and specificity in the diagnosis of keratoconus, especially the ESV. Key words: Keratoconus; Tomography, optical coherence; Corneal epithelial thickness parameters