This retrospective observational study was conducted at the Department of Ophthalmology and Visual Science in Seoul St. Mary’s Hospital, The Catholic University of Korea, and adhered to the tenets of the Declaration of Helsinki. All protocols were approved by the Institutional Review Board (IRB) of Seoul St. Mary’s Hospital. Owing to the retrospective nature of this study and the use of anonymized data, waiver of informed consent was granted by the IRB in accordance with the provisions of the IRB.
Seventy-five patients diagnosed with monocular BRVO at our clinic were included in our study, along with forty-five sex- and age-matched control eyes. All the participants were selected between September 2020 and August 2021 at Seoul St. Mary’s Hospital. A retrospective review of medical records was conducted, and exclusion criteria were applied as follows: (1) refractive errors of exceeding ± six diopters (spherical equivalent); (2) eyes with a history of ocular trauma, laser treatment, or intraocular surgery; (3) eyes with a history of intravitreal injections for other ocular diseases; (4) other systemic diseases that could affect the retina, except hypertension and diabetes mellitus; (5) other retinal diseases, including glaucoma, age-related macular degeneration, diabetic retinopathy, neurodegenerative disease, or other retinal diseases affecting the macular lesion; (6) media opacity that could affect image quality; and (7) any history of uveitis.
During the initial visit, demographic data, medical history, and ophthalmologic history were recorded. All participants underwent ocular examinations, including slit-lamp microscopy, dilated fundus examination, OCT, and OCTA. OCT and OCTA were performed continuously using the Topcon DRI Triton SS-OCT device with a 1050-nm wavelength light source and a scanning speed of 100,000 A-scans/s. BRVO was diagnosed when its typical characteristics (i.e., regional flame shift hemorrhage along with vessels and ME) were present on fundus examination and OCT images (as shown in Fig. 1e,f). BRVO eyes with vitreous hemorrhage and multiple vascular obstructions (e.g., hemi–central retinal vein occlusion) and eyes with major BRVO that did not affect macular lesions were excluded. All patients received intravitreal injection treatment to resolve ME. According to the injection protocol, anti-VEGF injections were administered to ME with intermittent usage of dexamethasone implants in unresponsive cases. The BRVO group (n = 75) was divided into recurrent and indolent BRVO subgroup. Patients who acquired a state of resolved ME without an intravitreal injection or with 1 to 2 injections in > 3 years were assigned to the indolent BRVO subgroup. Patients who received multiple intravitreal injections or developed persistent macula edema were assigned to the recurrent BRVO subgroup. On the basis of reports suggesting a high correlation between deep capillary plexus (DCP) lesions and ME and visual acuity16, 3.0 × 3.0-mm en-face OCT DCP macular scans were selected for analysis at the time of resolved ME, at least 6 months after the initial visit (Fig. 1g). The scan at the time of resolved ME was chosen to prevent the intraretinal fluids from affecting the OCT and OCTA signal strengths. Two experienced independent retinal specialists (Y-H.P. and B-E.H.) who were blinded to the other imaging findings and clinical histories evaluated all en-face OCT and OCTA images.
En-face structural OCT perivascular reflectivity measurement on the area of high signal strength on OCTA
All en-face OCT images in this study met a minimum image quality of 65, with no line artifacts or noise. Figure 1 shows the process of selecting a high signal strength (HSS) area on OCTA and calculating the perivascular reflectivity of the corresponding area in the en-face structural OCT images. The 3.0 × 3.0-mm (320 × 320 pixels) DCP images were obtained using the DCP slab, which was calculated using the OCTARA segmentation algorithm built into the Topcon imageNET software (Fig. 1a,b). The images were divided into four quadrants, and two quadrants were selected for comparison to identify regional differences: the obstructive and contralateral quadrants. Binarization with a threshold of mean pixel value + 2 standard deviations (SDs) was applied to the OCTA images (Fig. 1b,c)17. We used the “analyze particle” command in the Image J software (version 1.53a; https://imagej.nih.gov/ij/)18 to calculate all white particle–like objects bigger than three consecutive pixels (approximately 28 μm) on the OCTA images to designate the area of HSS. The HSS area was then applied to the corresponding structural en-face OCT images, and the perivascular mean reflectivity was measured in that area (Fig. 1d,h). We calculated the mean corrected perivascular reflectivity as the mean reflectivity on the HSS area/overall en-face OCT mean reflectivity. We repeated the same procedure for the quadrants of the matched controls. We chose to designate HSS as a continuous particle of three pixels or more because the lateral resolution of swept-source OCT (SS-OCT) used in this study was 20 μm and the size of the retinal arterioles and venules was 15 μm or larger. This approach minimized signal noise and provided a measurable appropriate size for the signal of three pixels or more.
On OCTA, the area in which blood flow is measured displayed brightly, and the final brightness (reflectivity) in a selected scan was determined by accumulating decorrelation signals of each scan depth19. The HSS area represented a blood-rich area in which a detection of blood flow overlapped. We calculated reflectivity only in the HSS area, which contained pixels larger than mean pixel values + 2 SD of each scan, because analyzing the reflectivity in an area in which blood flow is definite and abundant effectively reduces the confounding factors for structural en-face OCT reflectivity.
Choroidal thickness, foveal avascular zone parameter, deep capillary plexus vessel density, fluorescein angiography nonperfusion area measurement
Choroidal thickness (CT) was determined using the automatic built-in software within the SS-OCT device. Subfoveal CT was calculated by measuring the distance from the outer border of the RPE to the inner edge of the suprachoroidal space20. The CT at the foveal center was manually measured using digital calipers provided by the SS-OCT software. The Topcon imageNET software was used to automatically calculate the foveal avascular zone (FAZ) area (mm2), perimeter (mm), and circularity. The ImageJ software was utilized to measure vessel density on the DCP OCTA macula images. After manually excluding the FAZ area, the OCTA images were binarized using the mean threshold (automatic threshold), and the percentage of white pixels was calculated for the vessel density via the “analyze particle” command21. Central and overall nonperfusion areas (NAs) on fluorescein angiography (FA) were measured (Supplementary data 2).
Statistical analysis was performed using Statistical Package for the Social Sciences for Windows (version 24.0; SPSS, Inc., Chicago, IL, USA). One-way analyses of variance (ANOVAs) were used to assess the mean differences between recurrent BRVO, indolent BRVO, and corresponding control quadrants, followed by a post-hoc independent t-test for the mean corrected perivascular reflectivity. Bonferroni correction was performed for multiple comparisons. Intergrader reliability was calculated using intraclass correlation coefficient (ICC) analysis. Regression analysis was conducted for several possible factors, including the number of intravitreal anti-VEGF or dexamethasone injections per year, with the corrected mean perivascular reflectivity. To evaluate the effect of disease duration, sub-analysis was performed by dividing the period from the initial diagnosis to the time of OCT and OCTA scan acquisition into two groups (based on 3 years from the initial visit), using the independent t-test and regression analysis.
Owing to the retrospective nature of image analysis and anonymized data of this study, the need of informed consent procedures was waived by the Institutional Review Board (IRB) of Seoul St. Mary’s Hospital. Waiver of informed consent was granted by the IRB in accordance with the provisions of the IRB. All protocols were also approved by the IRB of Seoul St. Mary’s Hospital, The Catholic University of Korea (KC23RISI0232).
The provisions of IRB: The study corresponds to [waiver of informed consent process] for the following reasons in accordance with relevant domestic and international regulations.
Retrospective study of medical record
It is practically impossible to obtain consent from the study subject in the course of the study or has a serious impact on the validity of the study
There is no reason to estimate the subject’s refusal to consent, and even if consent is exempted, the risk to the subject is extremely low.