In this study, of the 93 eyes with FIPED, CNV was observed in 21 eyes. The prevalence of CNV was 22.6%, which was closer to the lower border reported in previous studies. Previous reports have confirmed the presence of CNV in 18.9-58% of chronic CSC cases [7, 8, 13].
Using OCTA, several studies have quantified vessel density and flow index , as well as CNV [15, 16]. Accurate segmentation is important to interpret and quantify OCTA findings. However, in eyes with retinal pathology such as chronic CSC, the margins of the retinal layer are distorted and precise boundary segmentation can be difficult. Although many researchers have attempted to improve the quality of automated segmentation in diseased eyes [17, 18], accurate automated segmentation is not achieved in all clinical cases. Therefore, manual correction of segmentation is often required [19, 20]. In cases of chronic CSC, most FIPEDs are known to be avascular, although CNV in FIPED has been reported [5, 6]. However, because of multiple RPE changes and dilated pachy-vessels of the choroid, it is often difficult to detect CNV on FAG or ICGA .
Recently, several studies on PED using en-face views in OCTA have been performed [8, 9, 13, 21]. However, analysis using en-face images may result in errors, such as motion artefacts, projection artefacts, layer segmentation errors, and flow signal masking that can occur during the calibration of projection artefacts. To complement this, cross-sectional OCTA obtained by adding the flow signal to the existing OCT B-scan with false code, was introduced. It is possible to observe the flow signal in the PED without being affected by the errors that may occur in creating the en-face image. This results in continuous sectional views on scrolling. In cases of PCV and PED in AMD, some studies using cross-sectional OCTA as well as en-face view have been published [22-25].
It is important that the entire morphology of a CNV lesion is thoroughly analysed to qualitatively define a choroidal neovascular network, based on the shape, branching, anastomoses, type of vessels termini, and presence of hypointense perilesional halo . However, there could be some errors in en-face OCTA due to the abovementioned difficulties. Since CNV is not a coplanar structure, it may show a different morphology at each level of depth. En-face OCTA provides depth-resolved images; therefore, manual confirmation of the cross-sectional B-scan allows a layer-by-layer tomographic visualisation of the entire neovascular feature.
This study is significant because of the identification of CNV on FIPED of chronic CSC using both en-face and cross-sectional OCTA. The CNV in FIPED was observed in 23 eyes on en-face OCTA and 21 eyes on cross-sectional OCTA. The diagnostic efficacy of both the methods was similar; however, eight cases showed discrepant results on en-face OCTA. Among them, five were false-positive cases, i.e., en-face OCTA detected the presence of CNV but there was no actual CNV in these eyes (Figure 2). Four cases were identified as projection artefacts and one case as a segmentation error with the choriocapillaris layer under FIPED. The remaining 3 eyes had actual CNV confirmed on cross-sectional OCTA, but no CNV was seen on en-face OCTA. The reason for the false negativity was the small size of PED that could not be detected on en-face OCTA and masked PED in the process of removing projection artefacts. A total of eight eyes showed discrepant results on en-face OCTA that could not be ignored, and cross-sectional OCTA was required to compensate for these errors. With cross-sectional OCTA, a more complete layer-by-layer analysis of the entire structure could be performed to detect the precise location of the CNV lesion relative to the RPE layer.
When FIPED is observed in chronic CSC, it is not necessary to consider anti-VEGF treatment for the possibility of type 1 CNV. In this study, CNV in FIPED was found in 21 out of 93 eyes, and less than one-third of cases of active CNV. Previous studies have reported that OCTA findings in PED were caused by the severe choriocapillaris alteration in those with AMD [16, 27]. However, the vascular signal in FIPED with chronic CSC seems to be due to compensatory choriocapillaris vascular remodelling owing to a weak Bruch's membrane. The CNV lesion described as a “darker halo” or total absence of choriocapillaris with loss of both the inner and deeper choroidal vessels encircling the CNV lesions could not be found in this study. Therefore, careful observation in these cases compared to AMD is recommended.
Limitations of this study are the retrospective design and relatively small sample size. Additionally, this study investigated the strength of cross-sectional views, and unlike for the en-face view, clinicians need to observe each CNV lesion using manual scrolling. In addition, longitudinal studies are needed to confirm changes in CNV lesions in FIPED in chronic CSC patients. However, this study has value in that it is the first study to analyse CNV in FIPED in chronic CSC patients using both en-face and cross-sectional OCTA.