title: Possible errors in the measurement of retinal lesions.
abstract: OBJECTIVE
  To determine the accuracy of the measurement of structure in the retina from fundus photographs.
  
  
  METHODS
  A model eye was developed to measure the retinal image size of the Zeiss fundus camera. A x 10 microscope objective with a focal length of 16.41 mm was used together with a microscope graticule.
  
  
  RESULTS
  Under emmetropic conditions the difference between the calculated and the measured magnification was 8.6%. The total change in magnification from myopia to hyperopia was -24.63% to +18.1%. When the camera position was altered with respect to the model eye by +/- 5 mm under myopic conditions the change in magnification was -4.5% and +6.8%. In the hyperopic condition the change was -5.6% to +4.6%.
  
  
  CONCLUSIONS
  Measuring the size of structure in the retina from photographs may therefore prove to be inaccurate but in some circumstances determining the percentage change in size may prove more reliable.
authors.affiliation: Cardiac Surgery Unit, Royal Postgraduate Medical School, London, United Kingdom.
authors.forename: J V
authors.initials: JV
authors.lastname: Arnold
authors.forename: J W
authors.initials: JW
authors.lastname: Gates
authors.forename: K M
authors.initials: KM
authors.lastname: Taylor
mesh_terms: D000818:Animals; D004285:Dogs; D005654:Fundus Oculi; D007091:Image Processing, Computer-Assisted; D008954:Models, Biological; D010781:Photography; D015203:Reproducibility of Results; D012164:Retinal Diseases / Q000175:diagnosis* / Q000473:pathology