Optical coherence tomography angiography of non-exudative choroidal neovascularization

Yan Ke Xue Bao 2016;31(4):243-245 ykxb.amegroups.com Age-related macular degeneration (AMD) has been classified in two groups, neovascular and non-neovascular, which historically has been synonymous with exudative and non-exudative, respectively. Neovascular AMD occurs when pathologic blood vessels, choroidal neovascularization (CNV), arise from the choroid and extend above Bruch’s membrane toward the outer retina. Often these vessels are exudative in nature, resulting in leakage of fluid, lipid exudate, or blood causing vision loss. The exudation from CNV allows detection as leakage with dye based angiography and as fluid with structural optical coherence tomography (OCT). In 2013, Querques et al. used multimodel imaging to detect treatment naïve quiescent CNV (1). This diagnosis requires presence of (I) moderate reflective material between an elevated retinal pigment epithelium and Bruch’s membrane on spectral domain OCT; (II) absence of fluid on OCT; (III) staining with fluorescein angiography; and (IV) a plaque identified with indocyanine green angiography. This study confirmed the existence of non-exudative neovascular AMD, and that exudation is not required for the presence of CNV. OCT angiography (OCTA), which can detect CNV as moving blood cells in the outer retinal slab (2) rather than relying on the presence of leakage on FA or fluid on OCT, is an ideal imaging modality to further study non-exudative CNV. In 2015, Palejwala et al. first described the use of OCTA to detect non-exudative CNV (3). In this study, 32 fellow eyes of patients with neovascular AMD were scanned using OCTA. Two cases of clinically silent non-exudative CNV were found as flow in the outer retinal slab without exudation on structural OCT and without leakage on fluorescein angiography. One case was followed longitudinally and over 8 months, the CNV vessel area enlarged by 20%, however, exudation never developed. Several other studies have subsequently further characterized non-exudative CNV using OCT angiography (4-7). The recent study by Carnevali et al. aimed to describe features of treatment naïve quiescent CNV (TNQ-CNV) and estimate the detection rate by OCTA (7). This was an observational case series comparing TNQ-CNV diagnosed by traditional imaging methods to those which could be imaged on commercially available OCTA, AngioPlex and AngioVue. A group of 22 eyes of 22 patients with drusenoid pigment epithelial detachment (PED) without vascular network on ICGA were used as negative controls. OCTA detected CNV in 18/22 study eyes and there were no false positive eyes. They concluded there was sensitivity of 81.8% (18/22 patients) and 100% specificity. The most common morphology was irregular, foveal sparing, with a nonvisible core and well-defined margin. While OCT angiography is a powerful tool, it is important to be aware of confounding projection artifact to avoid falsely identifying CNV. As light passes through moving red blood cells in the superficial retina, a flickering shadow is cast onto the deeper structures and is misinterpreted as moving red blood cells by OCT angiogram algorithms (8-11). One must Editorial