title: Scheimpflug image-processing method for accurate measurement of ocular surfaces.
abstract: OBJECTIVE
  To develop a method to process Scheimpflug images to estimate higher-order variations in ocular surfaces.
  
  
  METHODS
  New England College of Optometry, Boston, Massachusetts, USA.
  
  
  METHODS
  Zernike polynomial functions were used rather than lower-order surface functions to fit the ocular surfaces to evaluate higher-order variations. A related ray-tracing method was developed to correct optical distortion of the Scheimpflug image.
  
  
  RESULTS
  The new method to process Scheimpflug images showed higher-order variations in the posterior corneal surface. In a simulation, ignoring higher-order variations in the anterior corneal surface, as in previous studies, produced an error as high as 202% for some estimated Zernike coefficients of the posterior corneal surface.
  
  
  CONCLUSIONS
  The results indicate that it is necessary to correct refractive distortion in Scheimpflug images using higher-order surface functions and that the method developed in this study can be used to process scheimpflug images for measurement of ocular wavefront aberrations.
authors.affiliation: New England College of Optometry, Boston, Massachusetts 02115, USA. hej@neco.edu
authors.forename: Ji C
authors.initials: JC
authors.lastname: He
authors.forename: Yanwen
authors.initials: Y
authors.lastname: Fang
mesh_terms: D003315:Cornea / Q000033:anatomy & histology*; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods*; D015233:Models, Statistical; D008962:Models, Theoretical; D010781:Photography / Q000295:instrumentation*