title: Distribution of posterior corneal astigmatism according to axis orientation of anterior corneal astigmatism.
abstract: OBJECTIVE
  To investigate the distribution of posterior corneal astigmatism in eyes with with-the-rule (WTR) and against-the-rule (ATR) anterior corneal astigmatism.
  
  
  METHODS
  We retrospectively examined six hundred eight eyes of 608 healthy subjects (275 men and 333 women; mean age ± standard deviation, 55.3 ± 20.2 years). The magnitude and axis orientation of anterior and posterior corneal astigmatism were determined with a rotating Scheimpflug system (Pentacam HR, Oculus) when we divided the subjects into WTR and ATR anterior corneal astigmatism groups.
  
  
  RESULTS
  The mean magnitudes of anterior and posterior corneal astigmatism were 1.14 ± 0.76 diopters (D), and 0.37 ± 0.19 D, respectively. We found a significant correlation between the magnitudes of anterior and posterior corneal astigmatism (Pearson correlation coefficient r = 0.4739, P<0.001). In the WTR anterior astigmatism group, we found ATR astigmatism of the posterior corneal surface in 402 eyes (96.6%). In the ATR anterior astigmatism group, we found ATR posterior corneal astigmatism in 82 eyes (73.9%). Especially in eyes with ATR anterior corneal astigmatism of 1 D or more and 1.5 D or more, ATR posterior corneal astigmatism was found in 28 eyes (59.6%) and 9 eyes (42.9%), respectively.
  
  
  CONCLUSIONS
  WTR anterior astigmatism and ATR posterior astigmatism were found in approximately 68% and 91% of eyes, respectively. The magnitude and the axis orientation of posterior corneal astigmatism were not constant, especially in eyes having high ATR anterior corneal astigmatism, as is often the case in patients who have undergone toric IOL implantation.
authors.affiliation: Department of Ophthalmology, University of Kitasato School of Medicine, Kanagawa, Japan.
authors.forename: Toshiyuki
authors.initials: T
authors.lastname: Miyake
authors.affiliation: Department of Ophthalmology, University of Kitasato School of Medicine, Kanagawa, Japan.
authors.forename: Kimiya
authors.initials: K
authors.lastname: Shimizu
authors.affiliation: Department of Ophthalmology, University of Kitasato School of Medicine, Kanagawa, Japan.
authors.forename: Kazutaka
authors.initials: K
authors.lastname: Kamiya
mesh_terms: D000293:Adolescent; D000328:Adult; D017677:Age Distribution; D000368:Aged; D000369:Aged, 80 and over; D001251:Astigmatism / Q000175:diagnosis / Q000453:epidemiology*; D003315:Cornea / Q000473:pathology; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D012189:Retrospective Studies; D055815:Young Adult