To determine retinal nerve fiber layer (RNFL) thickness distribution and its related factors in a general population of 45 to 69 year olds in Iran

The present study is part of the second phase of the Shahroud Eye Cohort Study in which samples were selected through a multi-stage random cluster sampling. All study participants underwent vision measurement, refraction tests, slit lamp examination, and ophthalmoscopic fundus exam. Tests also included imaging with Cirrus HD-OCT 4000 and its RNFL thickness data were used in this study

Of the first phase participants, 4737 participated in the second phase. Mean RNFL thickness in the superior, inferior, nasal, and temporal quadrants were 92.47µm [95% confidence interval (CI): 92.14-92.80), 111.22µm (95% CI: 110.7-111.73), 118.93µm (95% CI 118.31-119.55), 74.83µm (95% CI 74.07-75.59) and 65.48µm (95% CI 65.06-65.90). Multiple linear regression models indicated that RNFL thickness in all quadrants decreased with aging, was lower in females (coefficient: -0.87 and p=0.015), decreased by 1.42µm (p <0.001) for each millimeter increase in axial length, and decreased by 0.41µm (P=0.041) for each diopter decrease in spherical equivalent refraction

RNFL thickness in the 45 to 69 year old Iranian population is lower compared to other studies. This difference should be noted in making disease diagnoses, particularly glaucoma. Also, there is a significant relationship between aging and RNFL thinning in all quadrants. People with short axial lengths, myopics, and females are at greater risk of RNFL thickness decline