title: Corneal and refractive error astigmatism in Singaporean schoolchildren: a vector-based Javal's rule.
abstract: BACKGROUND
  Traditional approaches to Javal's rule do not use data from subjects with oblique astigmatism and have not been used to make predictions about subjects with oblique astigmatism. Vector approaches to analyzing refractive error can circumvent these problems.
  
  
  METHODS
  Subjects were 993 Singaporean schoolchildren. We performed linear regression of refractive error astigmatism on corneal astigmatism, using J0 vectors to describe with-the-rule and against-the-rule astigmatism and J45 vectors to describe oblique astigmatism.
  
  
  RESULTS
  We obtained the following statistically significant regression relationships: RJ0 = 0.931 x CJ0 - 0.276 and RJ45 = 0.638 x CJ45 + 0.010, where R and C denote refractive error astigmatism and corneal astigmatism, respectively.
  
  
  CONCLUSIONS
  Our vector-based Javal's rule gives closer predictions of refractive astigmatism than the original Javal's rule and the simplified Javal's rule and can be applied in cases of corneal oblique astigmatism.
authors.affiliation: Singapore National Eye Centre. Louistong@hotmail.com
authors.forename: L
authors.initials: L
authors.lastname: Tong
authors.forename: A
authors.initials: A
authors.lastname: Carkeet
authors.forename: S M
authors.initials: SM
authors.lastname: Saw
authors.forename: D T
authors.initials: DT
authors.lastname: Tan
mesh_terms: D000293:Adolescent; D001251:Astigmatism / Q000175:diagnosis* / Q000208:ethnology; D002648:Child; D003315:Cornea / Q000473:pathology*; D005260:Female; D005544:Forecasting; D006801:Humans; D008297:Male; D009907:Optometry / Q000379:methods*; D012044:Regression Analysis; D012846:Singapore / Q000453:epidemiology