Diurnal Variations in Anterior and Posterior Corneal Thickness and Curvature in Healthy Eyes: Global and Sector-Based Metrics and Lifestyle Associations

This study aims to characterize diurnal changes in corneal geometry of the anterior and posterior cornea in healthy eyes using global and sector-based metrics, and to explore their associations with lifestyle-related factors. A prospective observational study of 109 eyes was conducted, measuring intraocular pressure (IOP), corneal thickness, volume, and global/sector-based keratometry at five time points over a 10 h period, alongside a lifestyle questionnaire. Results revealed significant diurnal decreases in IOP, central and minimum corneal thickness, and corneal volume (p ≤ 0.031). While posterior keratometry remained stable, anterior keratometry showed statistically significant but clinically negligible changes (amplitude of change ≤ 0.29 D), primarily within the central 4 mm and inferotemporal regions. Weak to moderate positive correlations were found between water and coffee intake, smoking, and changes in corneal thickness and volume, with no relevant effects on keratometric parameters. Overall, corneal thickness and volume exhibit significant diurnal reductions, whereas anterior keratometric changes are minimal and clinically irrelevant globally. These findings underscore the importance of considering the time of day when interpreting corneal measurements, as lifestyle factors appear to modulate corneal thickness but not curvature in healthy eyes.