This large cross-sectional study investigated the prevalence of vertical cup-to-disc ratio (vCDR) asymmetry in a diverse cohort of U.S. adults, and assessed whether this factor was predictive of glaucoma.
Study design
Subjects included 5,359 participants aged ≥40 years from the National Health and Nutrition Examination Survey (NHANES), a longitudinal comprehensive health study. Retinal images were used to assess vCDR asymmetry, calculated as the absolute value of the difference between both eyes. Visual field (VF) defects were measured using Frequency Doubling Technology (FDT) perimetry.
Subjects were defined as having "disc plus field defined glaucoma" by combining VF data with grading of glaucomatous disc features.
Outcomes
Among healthy individuals without glaucoma, the prevalence of vCDR asymmetry ≥0.2 and ≥0.3 was 2.12% and 0.14%, respectively. Each 10-year increase in age was independently associated with a 1.44-fold higher odds of vCDR asymmetry ≥0.2. The presence of vCDR ≥0.2 was higher among whites and patients over the age of 70.
Using a vCDR asymmetry cutoff of ≥0.2, the sensitivity and specificity for detecting disc plus field defined glaucoma were 22.7% and 97.7%, respectively, whereas the positive predictive value (PPV) was 7.0%. Increasing the vCDR cutoff to ≥0.3 increased the PPV to 37.7%.
Limitations
The NHANES database did not include IOP or neuroretinal rim thickness data, and vCDR was assessed with nonsteroscopic fundus photography rather than by comprehensive ophthalmologic examination. Additionally, VFs were not analyzed using standard automated perimetry, which is typically considered the gold-standard for glaucoma diagnosis.
Clinical significance
This study provides important information regarding the prevalence of vCDR asymmetry in a large, nationally representative sample. Although this study confirms the relationship between higher vCDR asymmetry and glaucoma prevalence, its utility for diagnosing glaucoma remains limited since even high degrees of vCDR asymmetry were not highly predictive of glaucoma. The PPV at the highest cutoff of vCDR asymmetry (≥0.3) was well below 50%.
This suggests that while the presence of vCDR asymmetry should initiate a more comprehensive work up—especially in individuals with additional risk factors—it should not be used as a screening metric for glaucoma, as asymmetry may be physiologic in many individuals.