Myopia affects retinal nerve fiber layer measurements as determined by optical coherence tomography

To determine whether increasing myopia is associated with thinner peripapillary retinal nerve fiber layer (RNFL) when measured by Stratus optical coherence tomography (OCT).

Observational cross-sectional study.

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.

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, P<0.001, superior R=-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 mum/1 mm of axial length, and 3 mum/1 D sphere.

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.