title: Orientation changes of the main corneal axes as a function of age.
abstract: OBJECTIVE
  The purpose of this study was to assess the orientation of the anterior and posterior corneal surfaces with respect to the keratometric axis in the three-dimensional space.
  
  
  METHODS
  A group of 407 normal corneas of 211 subjects with ages ranging from 4 to 79 years was analyzed by fitting their elevation topographies to a general three-axes ellipsoid model.
  
  
  RESULTS
  The resulting average tilt (-1.20 degrees) and tip (1.83 degrees) of the anterior surface are consistent with previous findings. In addition, we found that the posterior surface is also misaligned with the anterior by a similar amount. The cornea seems to rotate as a solid body by 2 minutes of arc per year.
  
  
  CONCLUSIONS
  The misalignment between the cornea and the keratometric axis increases as a function of age. This tiny, but significant (p < 0.005), rotation may have an important impact on optical quality because it could cause an important increase of the higher order aberrations of the cornea with age.
authors.affiliation: Instituto de Ciencia de Materiales de Aragón, Consejo Superior de Investigaciones Científicas and Universidad de Zaragoza, Zaragoza, Spain. rafaelnb@unizar.es
authors.forename: Rafael
authors.initials: R
authors.lastname: Navarro
authors.forename: Jos J
authors.initials: JJ
authors.lastname: Rozema
authors.forename: Marie-José
authors.initials: MJ
authors.lastname: Tassignon
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000375:Aging; D002648:Child; D002675:Child, Preschool; D003315:Cornea / Q000033:anatomy & histology*; D019781:Corneal Topography / Q000379:methods*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D012016:Reference Values; D015203:Reproducibility of Results; D055815:Young Adult