title: Measurement of optic nerve head parameters: comparison of optical coherence tomography with digital planimetry.
abstract: OBJECTIVE
  To compare the measurements of optic nerve head parameters from digital photographic images and optical coherence tomography (OCT) in normal children.
  
  
  METHODS
  The Sydney Childhood Eye Study assessed 1765 children aged 6 years from 34 randomly selected primary schools during 2003 to 2005. Optic nerve head parameters were measured from digital photographs captured using a Canon fundus camera (CF-60Uvi)/EOS 10D and OCT3 (Zeiss Stratus) using the "fast" optic disc protocol. Retinal images of 333 sequential child participants were graded using both methods and are included in analyses. Optic disc and cup area, vertical and horizontal disc and cup diameters, vertical and horizontal cup/disc diameter ratios, and cup/disc area ratios were calculated using both modalities. Magnification of the planimetric images was corrected using the Bengtsson formula.
  
  
  RESULTS
  Mean vertical and horizontal disc and cup diameter and mean disc and cup area, as measured using OCT (1.76, 1.50, 0.71, and 0.68 mm and 2.15 and 0.47 mm, respectively) were significantly (P<0.0001; cup area P=0.0014) smaller than when measured using digital photography (1.85, 1.66, 0.76, and 0.74 mm and 2.40 and 0.51 mm, respectively). All 3 cup/disc ratio measures did not vary significantly (P>0.05) between the 2 methods (0.41, 0.45, and 0.22 vs. 0.41, 0.44, and 0.21, respectively).
  
  
  CONCLUSIONS
  Linear and area measures by Stratus-OCT, compared with digital planimetry measurements, are around 10% smaller; however, all 3 cup/disc ratios were preserved. Where OCT produces unexpectedly small cup/disc ratios, manual viewing is advisable. However, OCT can be considered moderately reliable in measuring and monitoring cup/disc ratio in clinical settings.
authors.affiliation: Centre for Vision Research, Department of Ophthalmology, Westmead Millennium Institute, University of Sydney, Sydney, Australia.
authors.forename: Chameen
authors.initials: C
authors.lastname: Samarawickrama
authors.forename: Amy
authors.initials: A
authors.lastname: Pai
authors.forename: Son C
authors.initials: SC
authors.lastname: Huynh
authors.forename: George
authors.initials: G
authors.lastname: Burlutsky
authors.forename: Jost B
authors.initials: JB
authors.lastname: Jonas
authors.forename: Paul
authors.initials: P
authors.lastname: Mitchell
mesh_terms: D002648:Child; D003941:Diagnostic Techniques, Ophthalmological; D005260:Female; D005654:Fundus Oculi; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008297:Male; D009898:Optic Disk / Q000033:anatomy & histology*; D010781:Photography; D012016:Reference Values; D041623:Tomography, Optical Coherence / Q000592:standards