Purpose: To evaluate age-related changes in astigmatism of both corneal surfaces and the whole cornea.
Methods: 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).
Results: 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 ≥71 years groups, respectively.
Conclusions: 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.
From the *Department of Ophthalmology, Taipei Medical University Hospital, Taipei, Taiwan; †Department of Ophthalmology, Taipei Medical University, Taipei, Taiwan; ‡Department of Ophthalmology, Taipei City Hospital, Taipei, Taiwan; §Department of Ophthalmology, National Taiwan University Hospital, Taipei, Taiwan; and ¶Community Medicine Research Center and ∥Institute of Public Health, National Yang-Ming University, Taipei, Taiwan.
Received for publication March 2, 2009; revision received September 10, 2009; accepted September 17, 2009.
The authors have no proprietary or commercial interest in any materials mentioned in this article.
Reprints: Ching-Yao Tsai, MD, PhD, Department of Ophthalmology, Taipei City Hospital, 145 Zheng Zhou Rd, Taipei 103, Taiwan (e-mail: firstname.lastname@example.org).