title: Characteristics and appearance of the normal optic nerve head in 6-year-old children.
abstract: OBJECTIVE
  To document planimetric measures of normal optic nerve head parameters in 6-year-old children and to report prevalence and associations of common optic nerve signs.
  
  
  METHODS
  The Sydney Childhood Eye Study examined 1765 children aged 6 years. Complete retinal photographs were available for 1225 participants, captured using a digital camera. Optical coherence tomography optic-disc measurements were acquired using the 'fast' optic-disc protocol. Statistical analyses were conducted using SAS version 9.1.3.
  
  
  RESULTS
  The mean (95% CIs) planimetric optic-disc area was 2.29 mm(2) (2.27 to 2.32), mean cup area 0.48 mm(2) (0.47 to 0.50), mean vertical disc diameter 1.81 mm (1.80 to 1.82) and mean vertical cup diameter 0.72 mm (0.71 to 0.73), resulting in a mean vertical cup/disc ratio of 0.40 (0.39 to 0.40). Similarities existed between vertical, horizontal and area cup/disc ratios (p>0.05) measured by planimetry and optical coherence tomography, but only for vertical disc diameters between 1.75 and 1.96 mm. Visible lamina cribrosa pores were present in 4.9%. This sign was associated with larger optic nerve parameters. The prevalence of optic disc tilt and cyclotorsion was 1.6% and 8.7%, respectively, and the prevalence of α- and β-peripapillary atrophy was 43.3% and 20.2%, respectively. Neither sign was associated with myopia, after adjusting for age, sex and ethnicity, although eyes with β-peripapillary atrophy had a longer mean axial length (p=0.04). Cilioretinal arteries were present in 27% and tended to be located temporally.
  
  
  CONCLUSIONS
  The mean vertical cup/disc ratio was 0.4 in this 6-year-old sample. Planimetric optic nerve head measures and population prevalence findings for optic disc signs in this population could be regarded as normative data for ophthalmologists in clinical settings.
authors.affiliation: Department of Ophthalmology, Centre for Vision Research, Westmead Millennium Institute (Westmead Hospital), University of Sydney, Westmead, Australia.
authors.forename: Chameen
authors.initials: C
authors.lastname: Samarawickrama
authors.forename: Amy
authors.initials: A
authors.lastname: Pai
authors.forename: Yasser
authors.initials: Y
authors.lastname: Tariq
authors.forename: Paul R
authors.initials: PR
authors.lastname: Healey
authors.forename: Tien Y
authors.initials: TY
authors.lastname: Wong
authors.forename: Paul
authors.initials: P
authors.lastname: Mitchell
mesh_terms: D001284:Atrophy / Q000453:epidemiology / Q000473:pathology; D002648:Child; D005260:Female; D005451:Fluorescein Angiography / Q000379:methods* / Q000592:standards* / Q000706:statistics & numerical data; D006801:Humans; D008297:Male; D009898:Optic Disk / Q000033:anatomy & histology* / Q000473:pathology; D009901:Optic Nerve Diseases / Q000453:epidemiology / Q000473:pathology; D015995:Prevalence; D012016:Reference Values; D012590:Sclera / Q000033:anatomy & histology; D012727:Sex Characteristics; D041623:Tomography, Optical Coherence / Q000379:methods* / Q000592:standards* / Q000706:statistics & numerical data; D014102:Torsion Abnormality / Q000453:epidemiology / Q000473:pathology