Five-year changes in retinal nerve fibre layer thickness in the adult population: a population-based cohort study

Clinical relevance Distinguishing between the pathological thinning of the retinal nerve fibre layer (RNFL) and age-related reduction requires a comprehensive understanding of the longitudinal changes in RNFL thickness within a healthy population. Background To determine five-year changes in RNFL thickness and associated factors in people aged 45-69 years. Methods This report pertains to the second and third phases of the Shahroud Eye Cohort Study. Participants were recruited by a multi-stage cluster sampling in Shahroud, Iran. Data on demographic details, visual acuity, non-cycloplegic refraction, and slit-lamp biomicroscopy were collected. High-definition optical coherence tomography was employed for retinal imaging. Results A total of 1,524 eyes from 908 participants were examined. The average RNFL thickness was 92.2 +/- 8.5 (95% CI: 91.6 to 92.8) and 93.1 +/- 8.7 mu m (95% CI: 92.5 to 93.7) in the first and second phases with a five-year mean change of 0.95 +/- 4.15 mu m (95% CI: 0.70 to 1.20). The RNFL thickness mean changes in the superior, inferior, nasal, and temporal quadrants were 2.51 +/- 7.86 (95% CI: 2.01 to 3.02), 2.93 +/- 7.39 (95% CI: 2.56 to 3.29), -0.53 +/- 6.15 (95% CI: -0.84 to -0.21), and -1.01 +/- 4.67 mu m (95% CI: -1.27 to -0.75), respectively. The five-year changes in average RNFL thickness were inversely correlated with axial length (beta = -0.69, p < 0.001), mean keratometry (beta = -0.37, p = 0.017), and baseline RNFL thickness (beta = -0.617, p < 0.001). In hyperopic individuals, the increase in average RNFL thickness (beta = 0.65, p = 0.012) was significantly greater than in those with emmetropia. Macular volume (beta = 1.65, p < 0.001) showed a direct association with five-year changes in average RNFL thickness. Conclusion Over 5 years, RNFL thickness changes were clinically insignificant in the normal population. The mean RNFL thickness seems to remain stable unless there is ocular disease. However, increased axial length and steeper keratometric readings were linked to RNFL thinning. Those with thicker RNFL measurements were at higher risk of thinning over time.