ABSTRACTMeasurements of central and peripheral corneal thickness, corneal topography, and central corneal curvature were made for 21 subjects at hourly intervals for 12 hr of 1 day for each subject. Values for corneal radius and asphericity were obtained from keratometry and photokeratoscopy, and their stability throughout the day was evaluated. Corneal radius was observed to steepen during the day, whereas asphericity remained constant. Corneal thickness was measured by pachometry and was found to be at its thickest on first awakening. Corneal curvature and central corneal thickness were highly correlated; low correlation was found between corneal asphericity and central corneal thickness. Some subjects exhibited large fluctuations in one or all of the parameters considered.