Purpose: To assess how OCT-derived epithelial thickness–difference metrics relate to corneal topographic inferior–superior (IS) asymmetry and to identify the most informative annular zones and axis-defined sector-pair metrics. Setting: University of São Paulo Design: Prospective, comparative observational study Methods: In this IRB-approved study of consecutive patients undergoing refractive surgery screening (regardless of ultimate eligibility), we analyzed 526 eyes. Axial IS values from Placido-based topography defined four strata (negative, 0.0–1.0, 1.0–1.4, and >1.4 D). Twelve epithelial thickness–difference metrics (including axis-defined sector-pair differences) were computed from 9-mm OCT maps across the 2–5 mm, 2–7 mm, and 2–9 mm annuli. Associations between continuous IS and each metric were tested using Pearson correlation and linear regression across the full spectrum and within analyses anchored at the clinically established IS = 1.4 D reference. Results: The central 2–5 mm annulus yielded the strongest associations with IS. Correlations were weak and slightly positive for IS ≤1.4 D but became stronger and consistently negative for IS >1.4 D, most prominently along the inferotemporal–superonasal (IT–SN) axis (r = −0.62; P 1.4 D stratum. Conclusions: Using manually derived, zone- and axis-specific OCT epithelial thickness–difference metrics, we found a nonlinear association with topographic IS, with the most informative signal in the central 2–5 mm annulus and along the IT–SN axis. Clinically, central, axis-defined epithelial asymmetry may serve as an adjunct interpretive marker in higher-IS (or borderline) eyes, whereas low-IS eyes show weak and variable epithelial–IS coupling—potentially explaining the limited performance of epithelial metrics in low-asymmetry settings.
Santhiago et al. (2026) studied this question.