title: Effects of aging on anterior and posterior corneal astigmatism.
abstract: OBJECTIVE
  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 > or =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.
authors.affiliation: Department of Ophthalmology, Taipei Medical University Hospital, Taipei, Taiwan.
authors.forename: Jau-Der
authors.initials: JD
authors.lastname: Ho
authors.forename: Shiow-Wen
authors.initials: SW
authors.lastname: Liou
authors.forename: Ray Jui-Fang
authors.initials: RJ
authors.lastname: Tsai
authors.forename: Ching-Yao
authors.initials: CY
authors.lastname: Tsai
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000375:Aging / Q000502:physiology*; D000869:Anterior Eye Segment / Q000473:pathology; D001251:Astigmatism / Q000175:diagnosis* / Q000503:physiopathology; D003315:Cornea / Q000473:pathology*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D010781:Photography / Q000379:methods; D014792:Visual Acuity / Q000502:physiology; D055815:Young Adult