In this cross-sectional study, investigators examined whether OCT angiography (OCT-A) imaging could be used to distinguish between different optic neuropathies.
Study design
Researchers analyzed OCT-A images from 48 healthy eyes, 29 eyes with acute nonarteritic anterior ischemic optic neuropathy (NAION), 44 eyes with papilledema and 8 eyes with optic neuritis. Total vasculature density was calculated using commercially available software, whereas capillary density was quantified using a customized software to exclude major vessels.
Outcomes
The total vascular density was lower in all eyes with optic disc edema compared with normal eyes, with NAION being the lowest, followed by optic neuritis and papilledema (all P<0.0001).
After excluding large vessels, the capillary density was lower in NAION eyes compared with papilledema eyes (P<0.001). Papilledema eyes, however, did not have significantly different capillary density from normal eyes. This was attributed to papilledema causing obstruction of some large vessels leading to a lower total vascular density, but does not represent true ischemia.
Overall, the best discriminator of NAION and optic neuritis from papilledema was the whole-image capillary density using the customized software.
Limitations
Although the authors found a trend towards reduced peripapillary vessel density in NAION compared with optic neuritis, the difference was not statistically significant. This was attributed to the small sample size of optic neuritis eyes. There is also the concern of accurately detecting and measuring capillaries in the setting of severe optic disc edema, especially in the presence of peripapillary hemorrhages. The authors minimized this limitation by including patients with similar retinal nerve fiber layer thicknesses across the etiologies of optic disc edema.
Clinical significance
OCT-A is potentially helpful in distinguishing NAION-induced optic disc edema from other causes of disc edema, such as papilledema. This differentiation is made more robust by analyzing the whole-image capillary density using customized software to exclude the large blood vessels. A larger number of optic neuritis patients will be required to determine if OCT-A can reliably differentiate NAION from optic neuritis with disc edema.
Although not a primary aim of the study, the results also suggest that analyzing peripapillary capillaries with exclusion of the large blood vessels may help detect ischemia in the setting of papilledema.