Topographic analysis of the changes in corneal shape due to aging.

We studied the aging changes in corneal shape using corneal topography. Normal corneas (1,343) from 734 volunteers were examined by Topographic Modeling System-1 (TMS-1). All eyes were divided into eight groups according to age: (a) < 20 years of age and, respectively, in their (b) 20s, (c) 30s, (d) 40s, (e) 50s, (f) 60s, (g) 70s, and (h) > 80. The age-related changes in the averaged map of TMS-1 were evaluated. The findings noted in this map were confirmed by analyzing the data as well as by assessing the average-of-difference map. The averaged maps of subjects from < 20 years of age to the 40s showed a vertical bow-tie-rule astigmatism. In the maps of subjects in their 50s and 60s, the central steep area gradually extended horizontally until it became a round configuration. The maps of subjects in their 70s and > 80 revealed a horizontal oval-shaped steep area, suggesting against-the-rule astigmatism. The average-of-difference map demonstrated a marked corneal steepening at the horizontal meridians. In the data analysis of the averaged map, the mean refractive powers of the cornea increased with age. Moreover, the refractive powers in the horizontal meridians exceeded those in the vertical meridians when they were in the 60s, which verified against-the-rule astigmatic shift. In conclusion, normal cornea becomes steeper and shifts from with-the-rule to against-the-rule astigmatism with age.