Inferior-Superior Epithelial Thickness Difference: Zone-Specific Analysis Across Topographic Asymmetry

Area of Science:

• Ophthalmology
• Corneal Imaging
• Refractive Surgery

Background:

• Corneal topography is crucial for refractive surgery screening.
• Inferior-superior (IS) asymmetry is a key topographic parameter.
• Epithelial thickness variations can influence corneal biomechanics.

Purpose of the Study:

• To evaluate the relationship between OCT-derived epithelial thickness metrics and corneal topographic IS asymmetry.
• To identify optimal annular zones and axis-defined sectors for assessing epithelial asymmetry.

Main Methods:

• Analyzed 526 eyes from patients undergoing refractive surgery screening.
• Computed 12 epithelial thickness-difference metrics from OCT maps.
• Correlated metrics with Placido-based topographic IS values across different strata.

Main Results:

• The central 2-5 mm annulus showed the strongest association with IS.
• A negative correlation was observed for IS >1.4 D, especially along the inferotemporal-superonasal axis (r = -0.62).
• Epithelial deviations were clearer in eyes with higher IS values (>1.4 D).

Conclusions:

• A nonlinear association exists between OCT epithelial thickness metrics and topographic IS.
• Central, axis-defined epithelial asymmetry is a valuable marker in higher-IS eyes.
• Epithelial metrics have limited utility in low-asymmetry eyes due to weak coupling.