Background/aims To investigate the prevalence of, and factors associated with, errors in neuroretinal rim measurement by Cirrus high-definition (HD) spectral-domain optical coherence tomography (OCT) in myopic eyes.

Methods Neuroretinal rim thicknesses of 255 myopic eyes were measured by Cirrus HD-OCT. The prevalence of, and factors associated with, optic disc margin detection error and cup margin detection error were assessed by analysing 72 cross-sectional optic nerve head (ONH) images obtained at 5° intervals for each eye.

Results Among the 255 eyes, 45 (17.6%) had neuroretinal rim measurement errors; 29 (11.4%) had optic disc margin detection errors at the temporal (16 eyes), superior (11 eyes), and inferior (2 eyes) quadrants; 19 (7.5%) showed cup margin detection errors at the nasal (17 eyes) and temporal (2 eyes) quadrants; and 3 (1.2%) had both disc and cup margin detection errors. Errors in detection of temporal optic disc margin were associated with presence of parapapillary atrophy (PPA), higher myopia, and greater axial length (AL) (p<0.001). Cup margin detection errors were associated with vitreous opacities attached to the ONH surface or acute cup slope angles (p<0.001).

Conclusions Errors in neuroretinal rim measurement by Cirrus HD-OCT were found in myopic eyes, especially in eyes with PPA, higher myopia, greater AL, vitreous opacity or acute cup slope angle. These findings should be considered when interpreting neuroretinal rim thickness measured by Cirrus HD-OCT.