title: Application of linear regression to videokeratoscope data for tilted surfaces.
abstract: OBJECTIVE
  To investigate the use of linear regression analysis performed on the tabular data display of the EyeSys videokeratoscope (VK). When a radius squared vs distance squared scatterplot is produced from aspheric surface data the equivalent conic section can be deduced from the intercept and slope of the linear regression line. Non-linear plots are often produced. Linear regression may then be applied in a number of ways.
  
  
  METHODS
  Topographical data derived from both the EyeSys VK and a computer model of the instrument were analysed by three methods of linear regression. The resultant apical radii, p-values and predicted surface tilts were compared with known values.
  
  
  RESULTS
  The three methods predict different surface characteristics whose errors were found to vary depending upon the asphericity of the surface and its tilt.
  
  
  CONCLUSIONS
  Apical radius is most accurately predicted by linear regression method (1). Both p-value and tilt are best predicted by averaging the radius and position data for corresponding points in each semi-meridian before squaring the resultant points and performing linear regression (method 3).
authors.affiliation: Department of Optometry, University of Bradford, West Yorkshire, UK. w.a.douthwaite@bradford.ac.uk
authors.forename: William A
authors.initials: WA
authors.lastname: Douthwaite
mesh_terms: D003315:Cornea / Q000033:anatomy & histology*; D019781:Corneal Topography / Q000379:methods* / Q000592:standards; D006801:Humans; D012044:Regression Analysis; D012680:Sensitivity and Specificity; D014741:Video Recording