Retinal nerve fibre layer thickness in a general population in Iran.

BACKGROUND

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

DESIGN

Population-based cross-sectional study.

PARTICIPANTS

Of the 5190 participants of phase one of Shahroud Eye Cohort Study, 4737 participated in Phase two (participation rate = 91.3%).

METHODS

All study participants underwent visual acuity 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.

MAIN OUTCOME MEASURES: The overall RNFL thickness and the average RNFL thickness in different quadrants.

RESULTS

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

CONCLUSION

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 ageing and RNFL thinning in all quadrants. Longer axial length, myopia and male gender are associated with reduced RNFL thickness.