Effects of Aging on Anterior and Posterior Corneal Astigmatism

To evaluate age-related changes in astigmatism of both corneal surfaces and the whole cornea.The right eyes of 370 subjects were measured with a rotating Scheimpflug camera (Pentacam). Astigmatisms of the anterior and posterior corneal surfaces were determined. The total corneal astigmatism was derived using power vector summation and vergence tracing. Age-related changes to corneal astigmatism were evaluated using polar value analysis (both in diopter and millimeter).For the anterior and total cornea, the proportion of with-the-rule astigmatisms decreased and those of oblique and against-the-rule astigmatisms increased with age. For the posterior cornea, most eyes displayed against-the-rule astigmatisms in all age groups. There was a significant trend toward against-the-rule astigmatism associated with increasing age for both anterior and total corneal astigmatisms (mean changes of -0.18 and -0.16 diopters/5 years, respectively), and toward with the rule in posterior corneal astigmatism (a mean change of 0.022 diopters/5 years). Regarding shape changes, a "flat meridian toward a more vertical orientation" trend with increasing age for both the anterior and posterior corneal surfaces was observed (mean changes of 0.0295 and 0.0224 mm/5 years, respectively). The posterior corneal surface compensated for the astigmatism arising from the anterior corneal surface in 91.4% and 47.7% of eyes in the 21-30 and > or =71 years groups, respectively.There were age-related shifts toward against-the-rule and with-the-rule astigmatisms for the anterior and posterior corneal surfaces, respectively. The compensating effects of the posterior corneal surface on anterior corneal astigmatism decreased with advancing age.