African Descent and Glaucoma Evaluation Study: Asymmetry of Structural Measures in Normal Participants

Purpose: The purpose of the study is to determine the degree of intereye asymmetry of optic disc topography and retinal nerve fiber layer (RNFL) thickness in healthy individuals of African descent (AD) and European descent (ED). Design: Observational, clinical study. Methods: Five hundred nineteen healthy individuals (AD, n=262, mean age=44.9 years; ED, n=257, mean age=47.1 years) from the African Descent and Glaucoma Evaluation Study and Diagnostic Innovations in Glaucoma Study were tested using Heidelberg retina romograph (HRT), GDx variable corneal compensation (GDx-VCC), and standard, automated perimetry within 6 months of one another. HRT-II measurements included cup area, cup volume, rim area, and rim volume. GDx-VCC measurements included average RNFL thickness. Intereye asymmetry was calculated as the absolute value of the differences in measurements between the right and left eye. Results: AD participants showed significantly higher median asymmetry in cup volume and rim volume (P<0.001 and 0.033, respectively) compared with ED participants. The effect of race lost significance after adjustment for mean disc area and disc area asymmetry in multivariable models. Axial length asymmetry was not correlated with increased asymmetry in any of this study's asymmetry parameters. Normal ranges of asymmetry for the HRT-II measurements of cup area (up to 0.39mm(2)), cup volume (up to 0.15mm(3)), rim area (up to 0.45mm(2)), and rim volume (up to 0.22mm(3)) were derived, as were asymmetry ranges for GDx-VCC-measured average RNFL thickness (up to 6.25 mu m). Conclusions: The effect of race was no longer significant after adjustment for mean disc area and disc area asymmetry. Individuals with asymmetries with magnitudes greater than those of the normal ranges could be considered as suspicious for glaucoma.