Myopia appears to cause errors in OCT neuroretinal rim measurement

This prospective study found errors in OCT measurement of neuroretinal nerve tissue of myopic eyes. These errors were associated with axial length (AL), higher myopia, vitreous opacities and parapapillary atrophy (PPA).

While not earth-shattering, this study helps to reconfirm my belief that diagnostic testing can aid in glaucoma testing but should not be the sole variable. I think this study reinforces the idea that the clinical exam with stereo photography is still the gold standard.

The authors used Cirrus high-definition spectral-domain OCT to measure the neuroretinal rim thicknesses of 255 myopic eyes. The prevalence of and factors associated with optic disc and cup margin detection error were assessed by analyzing 72 cross-sectional optic nerve head (ONH) images obtained at 5° intervals for each eye.

Neuroretinal rim measurement errors were found in 17.6 percent of eyes. The errors were found in the temporal (16 eyes), superior (11 eyes) and inferior (2 eyes) quadrants; 19 eyes (7.5 percent) showed cup margin detection errors at the nasal (17 eyes) and temporal (2 eyes) quadrants, and three (1.2 percent) had both disc and cup margin detection errors. 

Errors in detection of temporal optic disc margin were associated with the presence of PPA, higher myopia and greater 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).

The authors note that an interesting finding of this study was lower prevalence of errors in optic disc margin detection in the inferior quadrant (0.8 percent) compared to the superior quadrant (4.3 percent). This finding may be associated with differences in optic disc margin structure, retinal vascular characteristics and OCT scan angle between superior and inferior quadrants. To verify these hypotheses, further studies are required.