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Determinants of optic disc characteristics in a general population: The Rotterdam Study
R S Ramrattan1, R C Wolfs, J B Jonas
1Department of Ophthalmology, Erasmus University Medical School, Rotterdam, The Netherlands.
Objective:
To determine whether age, gender, height, and refractive error are associated with optic disc morphology in a general elderly population.
Design:
Population-based, cross-sectional study.
Participants:
A total of 5114 subjects 55 years of age or older participated in this study, representing 76% of a population-based sample of 6777 ophthalmologically examined white patients from a geographically well-defined suburb in Rotterdam, The Netherlands.
Main Outcome Measures:
Disc area, neural rim area, cup area, vertical and horizontal cup-to-disc ratios, and parapapillary atrophy.
Methods:
Disc characteristics were measured on stereoscopic simultaneous optic disc transparencies using an image analyzer. The presence and location of parapapillary atrophy, differentiated into zones alpha and beta, were assessed from disc transparencies of both eyes in a random sample of 894 persons. Subjects with open-angle glaucoma were excluded.
Results:
The mean disc area was 2.42 mm2 (standard deviation [SD], 0.47), mean neural rim area was 1.85 mm2 (SD, 0.39), mean cup area was 0.57 mm2 (SD, 0.34), mean vertical cup-to-disc ratio was 0.49 (SD, 0.14), and mean horizontal cup-to-disc ratio was 0.40 (SD, 0.14). Age was not a determinant of any disc characteristic. Disc and rim areas were 3.2% (P < 0.0005; 95% confidence interval [CI], 2.7%-3.7%) and 4.3% (P < 0.0005; 95% CI, 3.5%-4.6%) larger in men than in women. For each diopter increase toward myopia, the disc area increased by 0.033 mm2 (P < 0.0005; 95% CI, 0.027-0.038) and neural rim area by 0.029 mm2 (P < 0.0005; 95% CI, 0.025-0.034). The disc area increased by 0.02 mm2 (P = 0.02; 95% CI, 0.005,0.05) for each 10-cm increase in height. The prevalence of zone alpha slightly decreased by 0.4% per 10 years of age (P = 0.035; 95% CI, 0.03%-0.8%), whereas the prevalence of zone beta increased by 1.3% (P = 0.0003; 95% CI, 0.57%-1.9%) for each diopter increase toward myopia.
Conclusions:
In a general population, statistically normal discs may vary twofold in disc area and threefold in rim area. Age is not associated with any disc characteristic, whereas disc area and neural rim area are slightly larger in men than in women. Refractive error is weakly related to disc area and neural rim area. Height is weakly related to disc area in persons of medium height. The prevalence of zone beta is higher in myopic eyes.