Measurement of corneal curvature in young and older normal subjects

PURPOSE: 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. METHODS: 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 m eridian in a group of young and older subjects using the EyeSys videokerato scope and the Topcon autokeratometer, RESULTS: With EyeSys data, horizontal vertex radius and p value were comput ed by means of plotting a graph of r(2) (sagittal radius) versus y(2) (perp endicular distance from the instrument optical axis). For Topcon data, prev iously derived equations were used. Mean vertex radii in the younger Topcon autokeratometer group was 7.91 +/- 0.31 and for the EyeSys videokeratoscop e 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 gr oup was 0.66 +/- 0.09 for the Topcon and 0.78 +/- 0.07 for the EyeSys. In t he older group, mean vertex radii was 0.74 +/- 0.07 for the Topcon and 0.86 +/- 0.07 for the EyeSys. CONCLUSION: Vertex radius decreased with age, demonstrating a steepening of the cornea, and confirming previous results. The p value increases with ag e, indicating a shift toward a more spherical surface. The rate of change i n the vertex radius and p value with age are predicted.