Distribution of Optic Disc Parameters Measured by OCT: Findings from a Population-Based Study of 6-Year-Old Australian Children

PURPOSE: To study the distribution of optic disc, cup, and neural rim size by ocular and demographic variables in a population-based sample of 6-year-old children. METHODS: The Sydney Childhood Eye Study examined 1765 of 2238 eligible 6-year-old children (78.9%) from 34 randomly selected Sydney schools during 2003 to 2004. Comprehensive standardized eye examination included cycloplegic autorefraction, optical biometry and "fast optic disc" scans performed using optical coherence tomography. RESULTS: Scans of adequate quality were available for 1309 children (75% of participants), with 70% aged 6 years; 50.9% were boys. Mean (+/- SD) horizontal and vertical disc diameter and disc area was 1.53 +/- 0.21 mm, 1.79 +/- 0.28 mm, and 2.20 +/- 0.39 mm(2), respectively. Corresponding cup dimensions were 0.70 +/- 0.28 mm, 0.73 +/- 0.27 mm, and 0.48 +/- 0.32 mm(2). A definable optic cup was absent in 7.4%, 87% of whom were European white. Cup-to-disc diameter ratios were 0.46 +/- 0.16 horizontally and 0.42 +/- 0.15 vertically, whereas cup-to-disc area ratio was 0.22 +/- 0.13. Mean +/- SD neural rim area was 1.76 +/- 0.44 mm(2) and increased with disc size (Pearson correlation = 0.68, P < 0.0001). Horizontal and vertical average nerve widths were 0.36 +/- 0.05 and 0.28 +/- 0.05 mm, respectively. In analyses adjusting for potential confounders, disc area increased significantly with axial length (P(trend) < 0.0001) and refraction (P(trend) = 0.02). Rim area increased only with axial length (P(trend) = 0.01). There were no gender differences, except for average nerve width, marginally greater in boys. Most disc and cup dimensions were significantly larger in East-Asian than European white and Middle Eastern children. CONCLUSIONS: Disc, cup, and neural rim parameters were generally normally distributed in this young population. Axial length appeared to be a stronger determinant of disc and rim size than refraction. Some ethnic but not gender differences were demonstrated for most parameters.