## 4 Discussion  
In the present study, the tumor boundary was clearly observed on en face images of SS-OCTA and was demarcated from adjacent normal choroidal vasculature including choriocapillaris (CC) and medium- and large-sized choroidal vessels. Compared with previous studies that monitored CO vasculature in the CC layer using relatively limited OCTA techniques [5; 9; 10; 19; 20; 21; 22], our result provides greater insight into the CO vasculature. Despite the advantages of OCTA over FA and ICGA, in terms of visualizing more detailed microvascular flow information at various levels in the retina and choroid, the imaging of blood flow from the choroidal Sattler's layer and Haller's layer is a challenge for OCTA because of scattering by the pigment of the RPE and by vessels in the CC, which results in lower signal strength and saturation, thereby impairing visualization [23]. TowardPi SS-OCTA offers improved visualization of medium- and large-sized choroidal vessels. Using this approach, the CO vasculature is distinct from normal choroidal structures, and the blood flow of the CO was found to be located mainly within the choriocapillaris and partly the Sattler's layer, which is consistent with an earlier histopathological study of CO that showed the tumor was located between the CC and the outer choroidal tissue [1]. Moreover, there were some decalcification areas of the osteoma, where overlying RPE hyperplasia or atrophied and discontinuous or compressed choroidal vessels, displaying no blood flow on the corresponding SS-OCTA B-scan; this was also consistent with previous histopathological findings that the choriocapillaris was narrowed and obliterated in most areas of focally depigmented RPE or clumps of pigment granules observed along Bruch's membrane and attached to the outer retinal layers [1; 24]. The major factor causing visual compromise from CO is the development of CNV, which is often associated with subretinal fluid and hemorrhage [25]. Detecting CNV in eyes with osteoma using traditional imaging (e.g., FA and ICGA) can be challenging because  
Figure 5: Multimodal imaging of patient 18 (see Table 1): (**a**) fundus photography shows a circumpapillary CO with macular involvement; (**b**) an en face image corresponding to (**e**); (**c**) the avascular layer and corresponding B-scan of SS-OCTA show hyperreflective tumor-like tissue (red arrow) above the disrupted Bruch’s membrane (green arrow) that shows blood flow without subretinal hemorrhage or fluid, which is not indicative of CNV but may be a precursor to active neovascularization; (**d**) the choriocapillaris layer of SS-OCTA shows the blood flow signal of the osteoma is located mainly within the choriocapillaris and partly the Sattler’s layer on the composite B-scan; (**e**) SS-OCTA segmentation covering the entire border of the osteoma on the aligned B-scan images shows the boundary of the tumor clearly demarcated from the adjacent vessels of the choroidal Sattler’s layer and Haller’s layer. of high tissue density within the tumor, and secondary RPE abnormalities that promote irregular and persistent hyperfluorescence; consequently, it is difficult to distinguish CNV from feeder vessels [21, 26]. OCTA is superior to FA and ICGA in terms of visualizing CNV, including the contour and shape of vessels [27]. Since first reported by [PERSON] in 2016 [5], several studies have described CNV in patients with CO, as detected by OCTA from a relatively small number of cases [8, 9, 10, 22, 28, 29]. Most studies were case reports that described the OCTA features of CO as tiny, isolated flow-network lesions between the outer retina and choriocapillaris, similar to type 1 or type 2 CNV [8, 22, 30]. However, [PERSON] et al. [16] hypothesized a vascular connection between CNV and the intrinsic feeder vessels of the CO. [PERSON] et al. [10] differentiated the vascular network of CNV from the intrinsic vasculature of the CO, and showed on OCTA the feeder vessels extending into the tumor from the surrounding choroid.