Study design and ethical statement
We retrospectively reviewed the medical records of 290 patients (328 eyes) with acute and chronic CSC who visited the Department of Ophthalmology at Hanyang University Hospital between February 1, 2016, and February 1, 2018. This study was conducted according to the tenets of the Declaration of Helsinki and was approved by the Institutional Review Board at Hanyang University Seoul Hospital.
Eyes with other retinal abnormalities, such as polypoidal choroidal vasculopathy, age-related macular degeneration, idiopathic choroidal neovascularisation or other retinal vascular diseases, intraocular inflammation, and posterior segmental tumour were excluded. In addition, we excluded patients who had steroid-induced CSC and organ transplant-associated CSC. According to the manufacturer’s recommendation , images of poor quality (image quality score lower than 45) provided by the onboard OCT software were excluded.
The definitions used in this study were adapted from previous reports . CSC was defined as a retinal disease characterised by serous detachment of the neurosensory retina secondary to one or more focal lesions of RPE . Chronic CSC was defined as presence of symptoms for more than six months, history of recurrence, background fundus change, such as atrophic retinal and RPE changes, visible drainage tract or other atypical dye leakages during FA initial examination [4, 13]. Intravitreal anti-Vascular endothelial growth factor (VEGF) injection and photodynamic therapy (PDT) history were not excluded from the study criteria.
FIPED was defined as a small, flat, and irregular surface PED on the OCT B-scan. Unlike semi-circular PED, RPE elevation is not large but the RPE layer is separated from Bruch’s membrane and a “double layer sign” is observed . The sub-RPE space at the site of FIPED showed either hypo-reflection (not optically filled) or at least partial hyper-reflection, as previously described .
Patients’ medical records were reviewed, including best-corrected visual acuity, spherical equivalent, dilated fundus biomicroscopy findings, and multimodal imaging data including OCT, FA, ICGA, and OCTA.
All subjects underwent OCT and OCTA with Swept-source optical coherence tomography (SS-OCT) (Deep range imaging OCT, Triton, Topcon, Tokyo, Japan). We identified the presence of FIPED on OCT B-scans (Topcon SS-OCT parameters: 100 KHz, A-scan rate, wavelength 1050 nm). This study used OCTA ratio analyses employed by Topcon, which is an intensity ratio analysis, not based on amplitude-decorrelation. A 3 x 3 mm volume scan was performed, and each B-scan’s position was automatically scanned four times. All OCT and OCTA assessments were performed by two trained retinal specialists (B.R.L. and S.J.A.) who were not aware of each other’s imaging findings. OCTA B-scans and the 3 x 3 mm OCTA macular cube scans were primarily reviewed for the detection of FIPED and the presence or absence of CNV at the site of the FIPED. If a 3 x 3 mm OCTA image did not show any FIPED, the findings were confirmed through evaluation of the 4.5 x 4.5 mm or 6 x 6 mm OCTA B-scans. FA and ICGA (F-10, Nidek, Tokyo, Japan) was also performed, and assessed by the two specialists (B.R.L. and S.J.A.).
Choroidal neovascularisation using en-face OCTA and cross-sectional OCTA
When FIPED was confirmed, the OCTA image was analysed to evaluate the presence of CNV in FIPED. Using OCTA software, the retinal layers and generated en-face images of the superficial plexus, deep plexus, avascular retina, and choriocapillaris were automatically segmented. The inner plexiform layer (IPL)/inner nuclear layer (INL) line and the Bruch’s membrane (BM) line were created by automated segmentation. Next, the en-face image of the outer retina (from 70.2 µm under IPL/INL line to BM line) and choriocapillaris (from BM line to 10.4 µm under BM line) was constructed. For en-face OCTA, these two images were analysed to evaluate the presence of CNV in FIPED.
The OCT B-scans were then combined with the corresponding en-face OCTA images, and scrolling was enabled through the sections similar to that of OCT cube scan. In the cross-sectional OCTA, we used the Angio-B view provided by the Topcon, which is an image that combines an OCT B-scan with a flow signal coated with a false-colour code. The cross-sectional view helped identify the flow signal in the FIPED by providing scrolling function. It was possible to distinguish between projection artefacts and the real flow signals by checking the sequential sections.
As diagnosed in other studies [8, 10, 14, 15], CNV was confirmed with comprehensive data; clinical history and multimodal imaging data including OCT, FA, ICGA, and OCTA.