title: Corneal thickness profile and posterior corneal astigmatism in normal corneas.
abstract: OBJECTIVE
  To analyze the influence of corneal thickness profile on posterior corneal astigmatism (PA).
  
  
  METHODS
  Prospective, observational study.
  
  
  METHODS
  We included 418 normal subjects (213 men and 205 women) ranging in age from 6 to 93 years (49.0 ± 23.4 years, mean ± standard deviation) in this study.
  
  
  METHODS
  Anterior and posterior corneal topography were evaluated using 3-dimensional anterior segment optical coherence tomography. Pericentral corneal thickness (PCT) in each quadrant (superior, inferior, nasal, and temporal) was measured, and average PCT in the vertical (superior + inferior) and horizontal (nasal + temporal) directions was calculated. Posterior corneal astigmatism was calculated as (1) assumed PA based on the anterior corneal curvature measurement and the keratometric index and (2) actual PA derived from the direct measurement of posterior corneal curvature.
  
  
  METHODS
  Corneal thickness distribution and the difference between assumed and actual PA.
  
  
  RESULTS
  The PCT was significantly greater in the vertical (546.0 ± 31.8 μm) than in the horizontal direction (542.6 ± 31.7 μm) (P < 0.0001), and the difference between them was significantly correlated with subject age (r = 0.518, P < 0.0001). The difference between assumed and actual PA significantly correlated with the discrepancy between vertical and horizontal PCT (r = 0.819, P < 0.0001), as well as subject age (r = 0.533, P < 0.0001).
  
  
  CONCLUSIONS
  Corneal thickness is greater in the vertical than in the horizontal direction, making the PA more against-the-rule pattern than calculated on the basis of the anterior corneal curvature measurement only. Such discrepancy is more prominent in older patients.
authors.affiliation: Department of Ophthalmology, University of Tsukuba Hospital, Ibaraki, Japan. Electronic address: yu_ueno71@yahoo.co.jp.
authors.forename: Yuta
authors.initials: Y
authors.lastname: Ueno
authors.affiliation: Department of Ophthalmology, Faculty of Medicine, University of Tsukuba, Ibaraki, Japan.
authors.forename: Takahiro
authors.initials: T
authors.lastname: Hiraoka
authors.affiliation: Department of Ophthalmology, University of Tsukuba Hospital, Ibaraki, Japan.
authors.forename: Maki
authors.initials: M
authors.lastname: Miyazaki
authors.affiliation: Ito Eye Clinic, Ibaraki, Japan.
authors.forename: Mutsuko
authors.initials: M
authors.lastname: Ito
authors.affiliation: Department of Ophthalmology, Faculty of Medicine, University of Tsukuba, Ibaraki, Japan.
authors.forename: Tetsuro
authors.initials: T
authors.lastname: Oshika
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000375:Aging / Q000502:physiology*; D001251:Astigmatism / Q000503:physiopathology*; D002648:Child; D003315:Cornea / Q000473:pathology*; D063171:Corneal Pachymetry; D019781:Corneal Topography; D005260:Female; D006801:Humans; D021621:Imaging, Three-Dimensional; D008297:Male; D008875:Middle Aged; D011446:Prospective Studies; D041623:Tomography, Optical Coherence