Myopia Affects Retinal Nerve Fiber Layer Measurements as Determined by Optical Coherence Tomography

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Abstract
Purpose To determine whether increasing myopia is associated with thinner peripapillary retinal nerve fiber layer (RNFL) when measured by Stratus optical coherence tomography (OCT). Design Observational cross-sectional study. Methods Normal subjects with myopia underwent refractometry, axial length measurement (IOL Master), optic nerve examination, and OCT (12 fast RNFL scans/eye). The more myopic eye was chosen as the study eye. Correlation coefficients were calculated for demographic and optic disk characteristics, and degree of myopia. Results Mean age (n=27) was 34±8 years (range: 23 to 54). Mean cup-to-disk ratio was 0.38 with 41% large and 59% medium disk size. Eight subjects had peripapillary atrophy and 6 had disk tilt. Mean spherical equivalent was −5.40 D (range: −1.25 to −11.25), with mean axial length of 25.65 mm (range: 22.63 to 27.92). No significant associations were found between RNFL thickness and age (P=0.20), sex, disk size, cup-to-disk ratio, tilt, or peripapillary atrophy. RNFL thickness decreased with higher axial length (overall R=−0.70, PR=−0.60, P=0.001, and inferior R=−0.60, P=0.001), and higher spherical equivalent (overall R=−0.52, P=0.005, superior R=−0.41, P=0.03, and inferior R=−0.45, P=0.02). Overall RNFL thickness decreased 7 μm/1 mm of axial length, and 3 μm/1 D sphere. Conclusions Moderately myopic subjects tend to have thin peripapillary RNFL, mainly at the superior and inferior poles, as measured by Stratus OCT. This phenomenon should be considered when interpreting a glaucoma suspect's Stratus OCT measurements compared with the normative database.

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