Race, Ethnicity Contribute to Differences in Retinal Nerve Fiber Layer Thickness

Researchers examining the differences in retinal nerve fiber layer (RNFL) thickness among healthy adults of minority groups in the United States found significant variance among Latino Americans, African Americans, and Chinese Americans. Their findings were published in Ophthalmology.

The researchers sought to promote proper clinical application and interpretation of optical coherence tomography (OCT)-based RNFL thickness measurements of individuals of minority populations, as they are underrepresented in normative reference databases.  They created a database of optic scans of 11,585 healthy eyes from 6133 individuals from 3 population-based cohort studies of similar design: the Los Angeles Latino eye study (LALES), the Chinese American eye study (CHES), and the African American eye disease study (AFEDS), from which they pooled epidemiological, ocular, and OCT imaging data for participants aged 50 years or older.

The researchers performed segmentation and calculated the RNFL thickness. They retained scans (1 per eye) with signal strength of at least 7 out of 10 for the analysis and no segmentation errors and excluded participants who had a diagnosis of glaucoma, diabetic retinopathy, macular degeneration and cataract related phenotypes or any history of glaucoma or cataract procedures. They also excluded any participants with extreme refractive error and those who had a difference of more than 30 µm in RNFL thickness between their eyes. 

The study authors used linear mixed models to assess the relationship between continuous RNFL thickness measures and demographic and clinical variables while allowing for relatedness between eyes by including a random effect in the model. They performed sensitivity analyses of higher-quality scans using a signal strength of at least 9 and randomly selecting 1 eye per participant and running regression models without a random intercept.

They compared the RNFL distributions in participants with glaucoma (521 participants with glaucoma or glaucoma suspect) to those in healthy participants.

The 6133 qualified participants (2210 males, 3923 females; 2843 Chinese Americans, 1979 Latinos, and 1311 African Americans) had a mean age of 60.1 years (standard deviation (SD): 7.4 years).

The researchers found that African Americans had thinner RNFL than Chinese Americans and Latino Americans (P <.05) across all quadrants, and the magnitude of differences was greatest in the temporal quadrant (mean difference = -13.47 and -4.18 µm between the groups, respectively). Latino Americans had thicker nasal RNFL and thinner temporal RNFL than Chinese Americans (P <.05) but had similar superior and inferior RNFL thickness. Chinese Americans had the largest cup-to-disc ratios (CDR) and largest disc area after adjusting for age and sex (P <.05).

Average and quadrant specific RNFL thickness were lower in older ages across all groups (P <.05), but estimated age-related differences in average RNFL thickness, especially in the nasal quadrant, were greatest in Latin Americans. Average RNFL thickness was 2.5 (95% confidence interval (CI): 1.8-3.1), 2.8 (95% CI: 2.3-3.3), and 3.5 (95% 18 CI: 2.9-4.1) µm thinner for African American, Chinese American, and Latin American groups respectively (age trend P <.05 and interaction P =.041) per each 10-year older age group.

Difference in average RNFL thickness remained after adjusting for axial length (AL), disc area, and other covariates in the multivariable regression.

Limitations of the study include not including Caucasian subjects as a comparison population and basing estimates of age-related loss in RNFL thickness on cross-sectional comparison rather than longitudinal data.

Reference

Nousome D, Mckean-Cowdin R, Richter GM, et al. Retinal nerve fiber layer thickness in healthy eyes of African, Chinese, and Latino Americans: a population-based multiethnic study. Ophthalmol. Published online November 17, 2020. doi: 10.1016/j.ophtha.2020.11.015