title: Comparing optic nerve-head-size measurements by the heidelberg retina tomograph with fundus photography performed with a novel focusing technique.
abstract: OBJECTIVE
  To compare disc areas as measured with the Heidelberg Retina Tomograph (HRT) to those obtained with a fundus camera.
  
  
  METHODS
  A nonrandomized comparative trial.
  
  
  METHODS
  Forty-six patients (88 eyes) who were participating in a glaucoma-screening study.
  
  
  METHODS
  Disc areas from fundus photographs taken with a Nidek nonmydriatic camera were measured in pixels (Adobe photoshop 7.0). A magnification factor was determined, using a previously described technique that uses the position of the focusing slide on the camera to account for the spherical refractive error. The resulting calculated disc areas were then compared with the disc areas as measured with the HRT.
  
  
  METHODS
  Disc area.
  
  
  RESULTS
  The limits of agreement between the 2 techniques were 0.49 and -0.51 mm2, indicating that the range of differences between these imaging techniques was approximately 1 mm2. Using a Bland-Altman plot, the distribution of residuals indicated that the 2 techniques do not differ in a systematic way.
  
  
  CONCLUSIONS
  Disc area measurements can be reasonably determined from digital fundus photography if corrected for focusing slide position when compared with HRT. This may have useful applications for both clinical glaucoma patient care and population-based glaucoma-screening programs.
authors.affiliation: Department of Ophthalmology, Royal Victoria Hospital, McGill University, Montreal, Quebec, Canada. quigley.wilson@sympatico.ca
authors.forename: Michael G
authors.initials: MG
authors.lastname: Quigley
authors.forename: Vivek
authors.initials: V
authors.lastname: Patel
authors.forename: Pascale
authors.initials: P
authors.lastname: Dubé
authors.forename: Walter
authors.initials: W
authors.lastname: Wittich
authors.forename: Paul
authors.initials: P
authors.lastname: Harasymowycz
mesh_terms: D003941:Diagnostic Techniques, Ophthalmological; D005901:Glaucoma / Q000175:diagnosis; D006801:Humans; D008875:Middle Aged; D009898:Optic Disk / Q000473:pathology*; D009901:Optic Nerve Diseases / Q000175:diagnosis*; D010781:Photography / Q000379:methods; D011446:Prospective Studies; D014054:Tomography / Q000379:methods