Objective: To evaluate the effect of low-to-moderate myopia on peripapillary retinal nerve fiber layer (RNFL) thickness measured by Topcon SD optical coherence tomography (OCT).

Methods: Cross-sectional study. Methods: Ophthalmology Department, Shifa Foundation Falahee Clinic, over a period of one year starting from June 2015. Methods: A total of 43 eyes of 43 patients, having mild to moderate myopic refractive error, were enrolled in the study. Refractive error/spherical equivalent was calculated. RNFL thickness was obtained from all four peripapillary quadrants: temporal, superior, nasal, and inferior; and 12 sub-quadrants using Topcon SD OCT. Pearson correlation coefficients (r) were calculated to evaluate relationships between the RNFL thickness and spherical equivalent (SE) before and after adjustment for ocular magnification.

Results: The study included 51.2% females and 48.8% males. Mean age was 30.9 ±6.45 years. Mean axial length was 24.25 ±0.91 mm. Mean SE was -3.25 ±1.93 DS. Mean of average RNFL thickness (with Littmann's correction) was 97.28 ±8.15 µm. Correlation analysis among all subjects showed that the average, mean nasal quadrant, upper nasal, and inferonasal sub-quadrant RNFL thickness had positive correlation with spherical equivalent (r = 0.31, p = 0.045).However, correction of the magnification effect by applying Littmann formula eliminated this effect.

Conclusions: In low-to-moderate myopia, RNFL measurements vary with refractive error of the eye. Since ocular magnification significantly affects the RNFL measurement, it should be considered in diagnosing glaucoma.