title: Algorithm for Purkinje images I and IV and limbus centre localization.
abstract: OBJECTIVE
  To develop a fast and reliable image processing algorithm for the extraction of Purkinje reflection data for measurement of ocular alignment with standard PC hardware.
  
  
  METHODS
  Purkinje images I and IV are specular reflections of light sources, the positions of which are proportional to eye rotation. Fast histogram-based thresholding and gradient techniques were used to localize Purkinje images I and IV, the pupil centre and the limbus centre in images obtained with near infrared light.
  
  
  CONCLUSIONS
  Execution time was 500 ms per eye. A set of 540 images was evaluated of which 94% were automatically analysed.
authors.affiliation: Department of Ophthalmology, Aachen University Hospital RWTH, Germany.
authors.forename: J C
authors.initials: JC
authors.lastname: Barry
authors.forename: U M
authors.initials: UM
authors.lastname: Pongs
authors.forename: W
authors.initials: W
authors.lastname: Hillen
mesh_terms: D000065:Accommodation, Ocular / Q000502:physiology*; D000465:Algorithms; D000550:Amblyopia / Q000517:prevention & control; D000869:Anterior Eye Segment / Q000033:anatomy & histology* / Q000502:physiology; D002648:Child; D002675:Child, Preschool; D003315:Cornea / Q000502:physiology; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods; D007223:Infant; D007259:Infrared Rays; D007908:Lens, Crystalline / Q000502:physiology; D008027:Light; D016850:Limbus Corneae / Q000033:anatomy & histology* / Q000502:physiology; D008838:Microcomputers; D011680:Pupil / Q000502:physiology; D012029:Refraction, Ocular / Q000502:physiology; D012030:Refractive Errors / Q000517:prevention & control; D015203:Reproducibility of Results; D012399:Rotation