Measurement of corneal curvature in young and older normal subjects

A decrease in the vertex radius occurs with aging. The aim of this study was to investigate whether the degree of flattening from the vertex to the periphery of the cornea, ie, the surface profile, also changes with age.

A "p" value (a parameter that denotes the rate of flattening from the apex to the limbus) and vertex radius were measured in the horizontal meridian in a group of young and older subjects using the EyeSys videokeratoscope and the Topcon autokeratometer.

With EyeSys data, horizontal vertex radius and p value were computed by means of plotting a graph of r2 (sagittal radius) versus y2 (perpendicular distance from the instrument optical axis). For Topcon data, previously derived equations were used. Mean vertex radii in the younger Topcon autokeratometer group was 7.91+/-0.31 and for the EyeSys videokeratoscope was 7.98+/-0.31. For the older group, Topcon mean vertex radii was 7.68+/-0.22 and EyeSys mean was 7.74+/-0.24. Mean p value in the younger group was 0.66+/-0.09 for the Topcon and 0.78+/-0.07 for the EyeSys. In the older group, mean vertex radii was 0.74+/-0.07 for the Topcon and 0.86+/-0.07 for the EyeSys.

Vertex radius decreased with age, demonstrating a steepening of the cornea, and confirming previous results. The p value increases with age, indicating a shift toward a more spherical surface. The rate of change in the vertex radius and p value with age are predicted.