Retinal Nerve Fiber Layer and Optic Nerve Head Parameters in a Healthy Iranian Population: A Spectral-Domain Optical Coherence Tomography Study

Purpose To establish normative reference intervals (RIs) for retinal nerve fiber layer (RNFL) and optic nerve head (ONH) parameters measured using spectral-domain optical coherence tomography (SD-OCT) in a healthy Iranian adult population. Methods This prospective, cross-sectional study recruited healthy adults from the PERSIAN Organizational Cohort Study in Mashhad. All participants underwent comprehensive ophthalmic examinations and ONH imaging using the Optovue RTVue XR Avanti SD-OCT system. Data quality was ensured through standardized acquisition procedures and exclusion of scans with artifacts or inadequate signal strength. Outliers were identified and removed using distribution-appropriate statistical methods. Reference intervals were established in accordance with CLSI C28-A3 guidelines using nonparametric or robust parametric approaches, with partitioning by sex and age applied when statistically justified. Results A total of 487 healthy adults (mean age: 40.5 ± 7.3 years; 56.5% male) were included in the final analysis. Significant sex-related differences were observed in several ONH parameters, with males showing larger disc and cup areas and females demonstrating greater rim area and rim volume. Age-related trends were also evident, including increasing cup-to-disc ratios and progressive declines in rim area, rim volume, and average RNFL thickness across older age groups. Conclusions This study provides a population-specific normative RI dataset for RNFL and ONH parameters in healthy Iranian adults. These reference intervals enhance the clinical utility of SD-OCT and support more accurate diagnosis of glaucoma and other optic neuropathies in this population.