Retinal nerve fiber layer thickness profile in an Iranian adult population

To determine the distribution of retinal nerve fiber layer thickness (RNFL) and its associated factors in a normal adult population using Spectralis spectral-domain (SD) optical coherence tomography (OCT). This research was conducted utilizing data from the third phase of the Shahroud Eye Cohort Study. Participants were selected from Shahroud City through a multi-stage cluster sampling technique. Uncorrected and best-corrected visual acuity, as well as refraction, were assessed for all participants. Subsequently, each individual underwent slit-lamp examinations conducted by an ophthalmologist. Following pupillary dilation with tropicamide 1% drops, fundoscopic examinations were carried out, and OCT imaging was performed using a Heidelberg Spectralis OCT device. A total of 3,700 eyes from 2,102 participants were included in this report. The average global RNFL thickness recorded in this study was 100.3 ‎µm‎ (95% CI: 99.9-100.7). When analyzed by sex, the average global RNFL thickness was 99.5 ‎ ‎µm‎ (95% CI: 98.9-100.1) for men and 100.9 ‎µm‎ (95% CI: 100.3-101.5) for women. Utilizing a multiple generalized estimating equations (GEE) model, the global RNFL thickness demonstrated a direct association with body mass index (β = 0.11; p = 0.013), corneal radius of curvature (β = 5.27; p < 0.001), and macular volume (β = 7.64; p < 0.001) while showing an inverse relationship with axial length (β=-2.29; p < 0.001), central macular thickness (β=-21.39; p = 0.002), and the presence of diabetes (β=-1.09; p = 0.009). The RNFL thickness profile within a normative cohort aged 50 to 74 years was demonstrated using Spectralis SD-OCT imaging. Beyond biometric indices, it is crucial to consider certain systemic factors that may influence RNFL thickness.