Effect of Myopia on the Thickness of the Retinal Nerve Fiber Layer Measured by Cirrus HD Optical Coherence Tomography

PURPOSE: To evaluate the effect of myopia on the peripapillary retinal nerve fiber layer (RNFL) thickness measured by Cirrus HD optical coherence tomography (OCT). METHODS: Comprehensive ophthalmic examinations were performed, including measurement of visual acuity, refraction, and axial length on 269 subjects (age, 19-26 years) with no ophthalmic abnormality. Further, 200 x 200-cube optic disc scans of the subjects' eyes were obtained with Cirrus HD OCT. The RNFL thickness at 256 points of the RNFL thickness profile and the average RNFL thickness were recorded. The correlations between these values and the axial length and spherical equivalent (SE) of refractive errors were then analyzed by simple linear regression, before and after adjustment of the ocular magnification. RESULTS: Before ocular magnification adjustment, the uncorrected average RNFL thickness decreased as the axial length increased and as the SE decreased. However, after the adjustment, the corrected average RNFL thickness exhibited no correlation with the spherical equivalent and a weak positive correlation with the axial length. Myopia also affected the RNFL thickness distribution. As the axial length increased and the spherical equivalent decreased, the thickness of the temporal peripapillary RNFL increased and that of the superior, superior nasal, inferior, and inferior nasal peripapillary RNFL decreased. CONCLUSIONS: The axial length affected the average RNFL thickness, and myopia affected the RNFL thickness distribution. High myopes are likely to exhibit different RNFL distribution patterns. Since ocular magnification significantly affects the RNFL measurement in such patients, it should be considered in diagnosing glaucoma.