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Editors Selection IGR 21-4
Clinical examination methods: Diagnostic accuracy of OCT-A
Comment by Toru Nakazawa on:
69318 Optical Coherence Tomography Angiography Vessel Density in Healthy, Glaucoma Suspect, and Glaucoma Eyes, Yarmohammadi A; Zangwill LM; Diniz-Filho A et al., Investigative Ophthalmology and Visual Science, 2016; 57: OCT451-9
Previous studies have demonstrated that ocular blood flow (OBF) is reduced in the optic nerve head, retina, choroid, and retrobulbar space in glaucoma. However, these studies were limited by the lack of a reproducible, accurate method to measure OBF, and could not determine whether changes in the microvasculature and in OBF have a causative role in the pathophysiology of glaucoma. Optical coherence tomography angiography (OCT-A) is a recently introduced imaging modality that can characterize the vasculature of each retinal layer and provide a quantitative assessment of microcirculation in the optic nerve head and the peripapillary region.
In this manuscript, the authors used SD-OCT (Avanti; Optovue, Inc.) and OCT-A (AngioVue; Optovue, Inc.) to compare retinal nerve fiber layer (RNFL) thickness in healthy subjects (n = 23), patients with suspected glaucoma (n = 37), and glaucoma patients (n = 104). Two vessel density measurements extracted from the RNFL data were analyzed with the standard AngioVue software: (1) circumpapillary vessel density (cpVD), measured in a 750-µm-wide elliptical annulus around the disc; and (2) whole image vessel density (wiVD), measured over the entire 4.5 x 4.5-mm image field.
The study found that age-adjusted mean vessel density was significantly lower in the OAG eyes than the glaucoma-suspected and healthy eyes (cpVD: 55.1%, 60.3%, and 64.2%, respectively; P < 0.001; and wiVD: 46.2%, 51.3%, and 56.6%, respectively; P < 0.001). The age-adjusted area under the receiver operating characteristic curve (AUROC) for differentiating between glaucoma and healthy eyes was highest for wiVD (0.94), followed by RNFL thickness (0.92) and cpVD (0.83). The AUROC for differentiating between healthy and glaucoma-suspected eyes was highest for wiVD (0.70), followed by cpVD (0.65) and RNFL thickness (0.65). Thus, OCT-A vessel density had a similar diagnostic accuracy as RNFL thickness measurements for differentiating between healthy and glaucoma eyes.
Importantly, this is the first report that has used OCT-A to evaluate the microvascular bed of the RNFL, which is the main site of damage in glaucoma. Moreover, the OCT-A measurements were not correlated to disc area, in contrast to other structural measurements, such as RNFL and optic nerve head parameters, which are influenced by optic disc size. While it should be noted that OCT-A does not directly measure blood flow, it should nevertheless provide an excellent imaging target for early glaucoma diagnosis and objective parameters for glaucoma assessment. Furthermore, OCT-A should open new avenues for research into the role of blood flow in the pathophysiology of glaucoma.
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