Peripapillary Retinal Nerve Fiber Layer (RNFL) Thickness Measurements by Topcon SD-OCT in Myopic Patients

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).

Cross-sectional study.

Ophthalmology Department, Shifa Foundation Falahee Clinic, over a period of one year starting from June 2015.

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.

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.

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.