Influence of Myopia on Size of Optic Nerve Head and Retinal Nerve Fiber Layer Thickness Measured by Spectral Domain Optical Coherence Tomography

PURPOSE: To investigate optic nerve head size and retinal nerve fiber layer (RNFL) thickness according to refractive status and axial length. METHODS: In a cross-sectional study, 252 eyes of 252 healthy volunteers underwent ocular biometry measurement as well as optic nerve head and RNFL imaging by spectral-domain optical coherence tomography. Correlation and linear regression analyses were performed for all subjects. The magnification effect was adjusted by the modified axial length method. RESULTS: Disc area and spherical equivalent were positively correlated (r = 0.225, r(2) = 0.051, p = 0.000). RNFL thickness showed significant correlations with spherical equivalent (r = 0.359, r(2) = 0.129, p = 0.000), axial length (r = -0.262, r(2) = 0.069, p = 0.000), disc radius (r = 0.359, r(2) = 0.129, p = 0.000), and radius of the scan circle (r = -0.262, r(2) = 0.069, p = 0.000). After adjustment for the magnification effect, those relationships were reversed; RNFL thickness showed negative correlation with spherical equivalent and disc radius, and positive correlation with axial length and radius of the scan circle. The distance between the disc margin and the scan circle was closely correlated with RNFL thickness (r = -0.359, r(2) = 0.129, p = 0.000), which showed a negative correlation with axial length (r = -0.262, r(2) = 0.069, p = 0.000). CONCLUSIONS: Optic disc radius and RNFL thickness decreased in more severely myopic eyes, but they increased after adjustment for magnification effect. The error due to the magnification effect and optic nerve head size difference might be factors that should be considered when interpreting optical coherence tomography results.