SHORT-TERM KERATOMETRIC VARIATION IN THE HUMAN EYE

Previous studies of corneal and keratometric variation used statistica l methods that were not entirely satisfactory. For the first time, pro per multivariate statistical methods are applied to evaluate short-ter m keratometric variation in human eyes. Keratometric variation is repr esented graphically by means of stereo-pair scatter plots, ellipsoidal confidence regions for mean dioptric power, and meridional profiles o f variation. There is great variability in the keratometric variation displayed by different subjects, although most subjects exhibit greate st variation in the vertical meridian of the eye on most of the measur ing occasions. Variance-covariance matrices based on vector h are give n. In some cases keratometric variation approaches neutral uniform var iation. In many of the subjects, mean keratometric measurements change from morning to afternoon, usually showing an increase in curvature l ater in the day. Physical activity may increase keratometric variation and mean curvature.