Corneal Geometry and Refractive Fluctuations Throughout the Day in Orthokeratology Wearers: A Preliminary Study

Despite the widespread use of orthokeratology (ortho-k), the diurnal behavior of corneal geometry after lens removal remains unclear. This prospective observational study evaluated diurnal variations in corneal geometry, refractive error, and visual performance in ortho-k wearers using global and sector-based corneal analyses. Nineteen eyes from ten ortho-k wearers were examined at five time points over a 10-h period following overnight lens wear. Corneal thickness, anterior and posterior corneal curvature, corneal asphericity, autorefractometry, and visual acuity were assessed. Corneal elevation data were reconstructed using Zernike polynomial expansions, and regional analyses were performed using concentric annular sectors. Diurnal amplitudes were compared with a healthy control cohort evaluated using the same protocol. Corneal thickness progressively decreased throughout the day (p < 0.001). Anterior corneal curvature showed progressive steepening (p ≤ 0.011), whereas posterior corneal curvature exhibited significant flattening (p ≤ 0.018). A progressive myopic refractive shift was also observed, with a spherical equivalent amplitude of −1.03 D (p = 0.002). Despite these changes, visual acuity remained stable (p = 0.248). Compared with healthy controls, ortho-k wearers showed greater amplitudes of central corneal thickness and anterior corneal curvature changes. These findings indicate that ortho-k may enhance normal diurnal corneal changes while maintaining visual acuity.