Background: Assessment of the optic disc and retinal nerve fiber layer (RNFL) is essential for the diagnosis and monitoring of glaucoma. Knowledge of normal optic disc topography provides a benchmark for evaluating glaucomatous pathologic changes, especially in its early stages. The purpose of this study was to evaluate the characteristics and correlation factors of the optic disc parameters using the Heidelberg Retina Tomograph II (HRT II) in a large sample of normal eyes of adult Chinese subjects.
Methods: Disc data were obtained from 6 830 subjects aged >30 years from the Handan Eye Study. All participants underwent comprehensive eye examinations and physical examinations. The associations of gender, age, body mass index, blood pressure, waist-to-hip ratio; refractive error, intraocular pressure, axial length, and disc area were assessed using simple and multiple regression analysis. The correlation between HRT II parameters was evaluated.
Results: Of the 7 557 eligible subjects, 6 830 took part in the study (90.4% response rate) and 2 633 normal eyes with good-quality HRT II images were selected. The mean disc area was 2.28 mm(2) (standard deviation (SD) 0.43) and mean neural rim area was 1.80 mm(2) (SD 0.29). In multiple regression analysis, optic disc area significantly correlated with age, gender, and axial length (P < 0.001). All optic disc parameters showed a significant correlation with disc area (0.054 <r <0.736, P < 0.01). The association between mean RNFL thickness and rim area is statistically significant but not strong (regression linear equation: rim area = 1.42 × mean RNFL thickness + 1.32 mm(2), P < 0.001; R(2) = 0.070). The global RNFL cross-sectional area was significantly associated with global rim area (regression linear equation: rim area = 1.14 × RNFL cross-sectional area + 0.44 mm(2), P < 0.001; R(2) = 0.271).
Conclusions: The optic disc area in rural Chinese population is larger than reported in white and Japanese populations, similar to that of Indian population and urban Chinese population. Most optic disc measurements were moderately or weakly affected by disc area. In addition to the RNFL, there may be other factors affecting the rim area. The relationship between optic disc and axial length may suggest a link between larger disc area, thinning of the lamina cribrosa, and increased glaucoma susceptibility in myopic eyes.