Regional corneal epithelial thickness and asymmetry patterns in early keratoconus versus regular astigmatism using MS-39 anterior segment OCT: a comparative cross-sectional study

Abstract

To compare corneal epithelial thickness (CET) profiles among different types of regular astigmatism and early keratoconus (KCN) using the MS-39 anterior segment optical coherence tomography (AS-OCT) and to identify disease-specific epithelial asymmetry patterns, regional epithelial thickness, and ROC performance. This comparative cross-sectional study included 96 eyes from 55 participants: with-the-rule astigmatism (WTR, n = 34), against-the-rule astigmatism (ATR, n = 19), oblique astigmatism (OBL, n = 13), and early keratoconus (KCN, n = 30). Corneal epithelial thickness maps and central corneal thickness (CCT) were obtained with the MS-39 AS-OCT. Because some participants contributed both eyes and group sizes were unequal, eye-level comparisons used participant-clustered robust standard errors. Multivariable models additionally adjusted for age, sex, cylinder power, and CCT. ROC 95% confidence intervals were estimated by participant-level cluster bootstrap. Regular astigmatic eyes showed the expected superior-to-inferior epithelial thickness gradient, whereas early KCN eyes showed relative superior epithelial thickening and attenuation of this gradient. CCT was lower in early KCN than in regular astigmatism (499.9 ± 29.3 μm vs. 555.7 ± 39.5 μm; P < 0.001). After adjustment for age, sex, cylinder power, and CCT, superior epithelial thickness remained greater in early KCN in the 2–5 mm annulus (adjusted B = + 2.78 μm; 95% CI, 1.15 to 4.41; P < 0.001) and 5–7 mm annulus (B = + 3.17 μm; 95% CI, 1.30 to 5.04; P < 0.001). The superior–inferior difference in the 2–5 mm zone also remained attenuated (B = + 2.10 μm; 95% CI, 0.51 to 3.68; P = 0.010). Superior ET at 2–5 mm had an AUC of 0.75 (95% CI, 0.62–0.87); a combined epithelial model yielded an AUC of 0.79 (95% CI, 0.67–0.90). Early KCN showed region-specific epithelial thickness differences characterized by relative superior epithelial thickening and attenuation of the normal vertical epithelial gradient. These differences persisted after adjustment for overall CCT, suggesting that the principal findings were not explained solely by differences in total corneal thickness. Diagnostic performance was moderate, so epithelial mapping should be considered an adjunct to established tomographic assessment.