Influence of myelinated retinal nerve fibers on retinal vessel density measurement with AngioVue OCT angiography.

Myelinated retinal nerve fibers (MRNF) represent an asymptomatic developmental anomaly in which myelin sheaths extend to a group of retinal nerve fibers along their intraocular portion. The additional volume of the myelin sheaths causes displacement of the axons toward the vitreous body. We investigated the effect of localized MRNF on peripapillary vessel density measurement results using optical coherence tomography (OCT) angiography. Peripapillary angioflow density measurements (PAFD, % of the analyzed retinal area) were made with the AngioVue OCT (Optovue Inc., Fremont, USA). In both cases, the predominant position of MRNF was inferonasal to the disk. Vessel density was clearly greater in the area of the MRNF than in the surrounding retina in the optic nerve head (ONH) level, but it was lower than in the surrounding retina in the retinal nerve fiber layer (RNFL) level. In the ONH level, PAFD was higher in the MRNF area than in the spatially corresponding superonasal area (Case 1: 64.6 vs. 57.6 %; Case 2: 65.8 vs. 56.3 %). In contrast, in the RNFL level, PAFD was lower in the MRNF area than in the corresponding superonasal area (Case 1: 60.1 vs. 65.4 %; Case 2: 46.5 vs. 58.5 %). Our cases show that the effect of MRNF on OCT angiography vessel density is different in the different measurement layers. Clinicians may separate decreased vessel density caused by anterior RNFL displacement in MRNF areas from that caused by nerve fiber damage in optic neuropathies by evaluating PAFD in both the ONH and RNFL levels.