Cup-to-Disc Ratio Asymmetry in U.S. Adults: Prevalence and Association with Glaucoma in the 2005–2008 National Health and Nutrition Examination Survey

Purpose To describe the prevalence of vertical cup-to-disc ratio (vCDR) asymmetry in U.S. adults and assess the utility of vCDR asymmetry in the diagnosis of glaucoma. Design Cross-sectional study. Participants A total of 5359 subjects aged ≥40 years from the 2005–2008 National Health and Nutrition Examination Survey (NHANES). Methods Subjects completed retinal photography and had vCDR determined in both eyes, with vCDR asymmetry calculated as the absolute value of the difference between the 2 eyes. Frequency Doubling Technology perimetry was used to assess for visual field (VF) defects. Subjects were categorized as having “disc defined glaucoma” if either disc demonstrated glaucomatous features, and VF data were combined with optic disc grading to determine “disc plus field defined glaucoma.” Main Outcome Measures Association between vCDR asymmetry and disc plus field defined glaucoma. Results In U.S. adults without glaucoma, the 50th, 97.5th, and 99.5th percentiles of vCDR asymmetry are 0.05, 0.19, and 0.26, respectively. Vertical cup-to-disc ratio asymmetry ≥0.20 occurs in 2.1% of U.S. adults without glaucoma. The prevalence of vCDR asymmetry ≥0.20 among white, black, and Hispanic adults without glaucoma is 2.4%, 0.7%, and 1.8%, respectively. The odds of vCDR asymmetry ≥0.20 are 1.44 times higher per 10-year increase in age (odds ratio [OR], 1.44; 95% confidence interval [CI], 1.20–1.72; P < 0.01). Each 0.10 increase in vCDR asymmetry was associated with a 2.57 times higher adjusted odds of disc plus field defined glaucoma (OR, 2.57; 95% CI, 1.43–4.61; P < 0.01). The sensitivity and specificity of vCDR asymmetry ≥0.20 for disc plus field defined glaucoma are 22.7% and 97.7%, respectively, whereas the positive likelihood ratio is 9.9 and the positive predictive value (PPV) is 7.0%. At a higher vCDR asymmetry cutoff of ≥0.30, the PPV increases to 37.7%. Conclusions Vertical cup-to-disc ratio asymmetry is predictive of prevalent glaucoma, but the PPV remains low even at high degrees of asymmetry. Vertical cup-to-disc ratio asymmetry should initiate a more comprehensive glaucoma workup, especially in individuals with additional risk factors, but it is not appropriate as a screening metric for glaucoma.