title: Optic disc measurement: a comparison of indirect ophthalmoscopic methods.
abstract: OBJECTIVE
  Two methods of indirect ophthalmoscopic estimation of optic disc size, the 78 dioptre lens and optic disc biometer were evaluated.
  
  
  METHODS
  Twenty nine eyes of 29 patients were measured by both methods and compared with optic disc size calculated using the three planimetric corrections described by Bengtsson and Krakau.
  
  
  RESULTS
  The closest agreement with the clinical measurements was found using correction 3. There was a significant difference between both the 78 D lens (p < 0.0001) and the biometer (p = 0.0027) and the planimetric results. There was also a significant difference between the two clinical methods (p < 0.0001). Both methods showed acceptable intraobserver variation (CoV 2.45% and 3.13% respectively).
  
  
  CONCLUSIONS
  Overall, both methods give larger measurements than planimetry; the 78 D lens by 0.41 mm and the biometer by 0.15 mm. Neither method gives a satisfactory estimation of optic disc size when compared with planimetry.
mesh_terms: D001699:Biometry; D003315:Cornea / Q000473:pathology; D005901:Glaucoma / Q000473:pathology; D006801:Humans; D015588:Observer Variation; D009798:Ocular Hypertension / Q000473:pathology*; D009887:Ophthalmoscopy / Q000379:methods*; D009898:Optic Disk / Q000473:pathology*; D012029:Refraction, Ocular