The ageing effect on the central posterior corneal radius

The posterior corneal radii along the vertical and horizontal meridians wer e measured using the Purkinje image technique. Two-hundred and forty subjec ts were recruited and divided into four different age groups (mean age of 2 0, 33, 41 and 50 years, respectively). Male and female subjects were nearly equally distributed in each group. A significant correlation was found bet ween the anterior and posterior corneas, along both the vertical (r = 0.83, P < 0.01) and horizontal (r = 0.89, P < 0.01) meridians. Ageing has a sign ificant effect on the horizontal meridian but not on the vertical meridian. The radii reduced with age and this phenomenon applied to both the anterio r and posterior corneas, gives rise to a more spherical cornea in advancing age. The posterior cornea has a surface power around 13% of the anterior c orneal surface, which indicates that the use of keratometer index 1.3375 is valid in estimating the total corneal power from the anterior corneal radi us. More information about the anterior and posterior corneas could be usef ul in the proposal of a four-surface schematic eye. (C) 1999 The College of Optometrists. Published by Elsevier Science Ltd. All rights reserved.