Biological and Methodological Variability in Retinal Nerve Fiber Layer OCT: The Framingham Heart Study

Objective: To explore participant-level biological attributes and scan-level methodological attributes associated with retinal nerve fiber layer (RNFL) thickness variability in a population-based sample of elderly United States adults. Design: Cross-sectional analysis using data from the Framingham Heart Study. Participants: One thousand three hundred forty-seven eyes from 825 participants with ≥1 OCT scan and axial length data were included. Methods: Three or more successive RNFL scans of each eye of each participant were obtained in a single session. Multivariable linear mixed models were employed to explore the associations between average RNFL thickness with participant-level biological attributes (age, gender, race, ethnicity, and axial length) and scan-level attributes (signal strength [SS]) as independent variables in the whole population as well as a subsample of adults with no self-reported history of glaucoma. Similar analyses were designed to assess methodological variability with average within-eye standard deviation (SD) for repeated scans as the dependent variable. Main Outcomes Measures: (1) Biological variability: average RNFL thickness, and (2) methodological variability: average within-participant SD across repeated scans. Results: Age (β = −0.19 microns/year, [95% confidence interval {CI}: −0.29, −0.09]), female gender (β = +1.48 microns vs. male, [95% CI: 0.09, 2.86]), axial length (β = −1.24 microns/mm of greater length, [95% CI: −1.80, −0.67]), and SS (β = +1.62 microns/1 unit greater SS, [95% CI: 1.16, 2.09]) were significantly associated with RNFL thickness, while race and ethnicity were not (P > 0.05). In analyses designed to assess methodological variability, higher RNFL thickness (β = +0.02 per micron increase, [95% CI: 0.01, 0.03]), and lower SS (β = +0.19 per 1 unit lower SS, [95% CI: 0.10, 0.27]) were significantly associated with greater RNFL variability. In adults with no self-reported history of glaucoma (n of eyes = 1165, n of participants = 712), female gender was not associated with RNFL, while African American race was associated with thicker RNFL (β = +4.65 microns vs. Whites, [95% CI: 1.28, 8.03]). Conclusions: Retinal nerve fiber layer thickness is lower with older age, male gender, greater axial length, lower SS, and Whites (as compared with African Americans) without self-reported glaucoma. Measurement variability (SD) is higher with greater RNFL thickness and lower SS. Understanding these biological and methodological variations is important to aid in OCT interpretation. Financial Disclosure(s): Proprietary or commercial disclosure may be found in the Footnotes and Disclosures at the end of this article.