Please see our prior studies
15–18 for a detailed description of OCT-A image acquisition. In brief, a 4.5- × 4.5-mm rectangle scan centered on the optic disc was used to record OCT-A images (with signal strength index of more than 48) using the AngioVue split spectrum amplitude-decorrelation angiography (SSADA) algorithm. Both large vessel and capillary densities from the internal limiting membrane (ILM) to the RNFL posterior boundary are imaged by the standard AngioVue software, and this measurement has been termed the retinal peripapillary capillary density (RPC) image. In this article, we used inner retinal vessel density (irVD) term for this type of image. Total peripapillary vascular (capillary and large vessels) density from ILM to RPE also was recorded and termed ONH image, and we used total retinal thickness vessel density (trVD) for this image. Total peripapillary (between commercially placed concentric circles) and its six sector (superotemporal, superonasal, temporal, nasal, inferotemporal, and inferonasal) vascular density values in irVD and trVD were reported (
Figs. 1,
2). We then used customized software
15–18 to determine “actual” capillary density in the same layers. OCT-A images (both irVD and trVD) were analyzed using a custom MATLAB program (The Mathworks, Inc., Natick, MA, USA) to calculate whole image capillary and peripapillary capillary densities (PCD) as we described before.
16 In summary, after placing two concentric circles with 3.45- and 1.95-mm diameters and removing large vessel signals, capillary density was calculated in both irVD and trVD images using a thresholding technique. Whole image capillary density (including the disc area) and PCD (between the two rings, excluding the disc area) were measured.
18 The PCD ring was also divided into four sectors (superior, inferior, nasal, and temporal), and their values were reported (
Fig. 2).