Subjects

The study was approved by the institutional review board of Wills Eye Hospital and complied with the Health Insurance Portability and Accountability Act. Patients with a diagnosis of BRVO who underwent OCTA of both eyes at the Retina Service of Wills Eye Hospital between January 1, 2015 and April 30, 2015 were retrospectively evaluated. Data collected included the findings of the comprehensive ophthalmologic examination, best-corrected visual acuity (BCVA) based on current spectacle correction with pinhole, and spectral-domain OCT (SDOCT, Spectralis; Heidelberg Engineering, Heidelberg, Germany). Fundus examination had been performed in each patient to confirm the diagnosis of BRVO and exclude any retinal vascular disease in the fellow eyes.

Inclusion and Exclusion Criteria

Patients with the diagnosis of BRVO involving the macula based on clinical examination were retrospectively enrolled. The diagnosis was confirmed using imaging studies (FA and/or SDOCT). Both treatment-naïve and previously treated patients were included. Patients were excluded if they had previous retinal surgery (prior vitrectomy), diabetic retinopathy, age-related macular degeneration, or other retinal vascular diseases.

Optical Coherence Tomography Angiography Image Acquisition

The AngioVue OCTA system on the commercially available Avanti SDOCT device (RTVue-XR Avanti; Optovue, Fremont, California, USA) was used for imaging. This system used an SSADA software algorithm (version 2015.100.0.35) and operated at 70 000 A-scans per second to acquire OCTA volumes consisting of 304 × 304 A-scans. Orthogonal registration and merging of 2 consecutive scans were used to obtain OCTA volume scans over a central 3 × 3 mm area of both eyes for each subject. OCTA images of the superficial and deep vascular networks were generated separately using the automated software algorithm. Based on these default settings, the boundaries of the superficial network extended from 3 μm below the internal limiting membrane to 15 μm below the inner plexiform layer (IPL). The deep capillary network extended from 15 μm to 70 μm below the IPL.

Two experienced independent graders (W.A.S., A.S.) reviewed the images. Patients with poor image quality were excluded based on 1 or more of the following criteria: low signal strength index (less than 50), presence of blink artifacts, poor fixation leading to motion or doubling artifacts, and media opacity obscuring view of the vasculature.

Foveal Avascular Zone, Foveal Thickness, and Vascular Density Measurement

Using the acquired images, measurements of the FAZ area were calculated using the non-flow function on the OCTA software ( Figure 1 ). The OCTA software uses a custom grid overlay that is superimposed on the 3 × 3 mm OCTA scan to generate vascular density in the different areas of interest ( Figure 2 ). The grid is composed of 2 circles: an inner circle with a diameter of 1 mm and an outer circle with a diameter of 2.5 mm. The foveal region was defined as the inner circle. The outer circle is also divided into sectors (nasal, temporal, superior, inferior). The foveal thickness was calculated from the inner circle. Vascular density values were calculated for the entire en face scan and for different sectors of the grid, as shown in Figure 2 . This calculation was performed by converting the obtained images to a binary format using an automated thresholding algorithm. Vascular density was calculated as the percentage area occupied by blood vessels, with the blood vessels being defined as pixels having decorrelation values above the threshold level. In BRVO eyes we compared the vascular density between the affected sector (superior or inferior) on the grid and the opposite unaffected sector of the same eye. We also compared both sectors with the corresponding sectors in the fellow eyes. Color-coded density maps were also generated through the SSADA algorithm, which localized areas with decreased vascular density ( Figure 2 ).

Foveal avascular zone (FAZ) measurement using optical coherence tomography angiography (OCTA) in an eye affected by branch retinal vein occlusion. A 3 × 3 mm OCTA scan centered on the macula at the level of the superficial (Top left) and deep (Top right) vascular networks. In both scans, irregular enlargement of the FAZ is seen, with black areas representing intraretinal edema that is more evident at the level of the deep vascular network (Top right, arrows). An automated software algorithm graphically highlighted and calculated the FAZ area in the superficial (Middle left) and the deep (Middle right) networks. The respective cross-sectional references are shown on the B-scans for the superficial (Bottom left) and the deep (Bottom right) vascular networks.

Macular vascular density measurement using optical coherence tomography angiography (OCTA) in an eye affected by branch retinal vein occlusion. (Top left) A 3 × 3 mm OCTA scan of the macula at the level of the superficial vascular network showing an area of non-flow superiorly. (Top middle) The vascular density in the superficial network was measured in the whole scan and in each sector of the grid. (Top right) Color-coded vascular density map is shown with dark blue areas corresponding to areas of non-flow. (Bottom left) A 3 × 3 mm OCTA scan of the macula at the level of the deep vascular network with an area of non-flow in the same distribution as seen in the superficial vascular network. (Bottom middle) The vascular density in the deep network was also measured in the whole scan and in each sector of the grid. (Bottom right) A color-coded map was generated after each scan to more easily identify areas of non-flow.

Statistical Analysis

BCVA was converted to the logarithm of the minimal angle of resolution (logMAR) for statistical evaluation. Statistical analyses were performed with SPSS, Version 20 (SPSS, Inc, Chicago, Illinois, USA). The paired t test was used to compare the logMAR visual acuity, vascular density, foveal thickness, and FAZ area between BRVO eyes and fellow eyes. The Pearson correlation coefficient was used to study the correlation between logMAR visual acuity, vascular density, FAZ area, and foveal thickness. A 2-tailed P value of <.05 was considered statistically significant.