Epithelial thickness ratio: a quantitative OCT-based metric for characterizing epithelial remodelling in keratoconus

OBJECTIVE: To develop and evaluate an optical coherence tomography (OCT)-derived metric, the epithelial thickness ratio (ETR), for distinguishing eyes with keratoconus from normal eyes. DESIGN: A retrospective proof-of-concept chart review. PARTICIPANTS: Twenty-seven normal eyes from 27 patients and 18 eyes with keratoconus from 18 patients were included. Normal eyes were selected from a refractive surgery practice, whereas eyes with keratoconus were selected from a hospital-based corneal specialty clinic over the same 1-year period. METHODS: Six ETR configurations were evaluated. ETR was calculated by averaging epithelial thickness at either 4 or 8 equidistant peripheral points centred on the corneal thinnest pachymetric location, at radii of 1.0, 1.5, or 2.0 mm, and expressing this value as a ratio to epithelial thickness at the thinnest point. ETR values were compared between normal eyes and those with keratoconus, and diagnostic performance was assessed using receiver operating characteristic (ROC) curve analysis. RESULTS: All ETR configurations were significantly higher in eyes with keratoconus than in normal eyes (all p ≤ .0002). Across configurations, area under the ROC (AUROC) curve values ranged from 0.813 to 0.879, indicating good discriminatory performance. The highest AUROC was observed for the 8-point, 2.0-mm radius configuration (AUROC 0.879, 95% CI: 0.741-1.000; p < .0001). CONCLUSIONS: In this proof-of-concept study, ETR differentiated clinically diagnosed keratoconus from normal corneas, supporting its potential role as an objective descriptor of ectasia-associated epithelial remodeling. Further prospective validation is required before ETR can be applied to subclinical ectasia detection or refractive surgery screening.