###### Abstract  
Choroidal neovascularization (CNV) secondary to choroidal osteoma (CO) can cause profound visual loss, but detecting CNV and the tumor's feeder vessels using traditional fluorescent angiography imaging is challenging. Newly developed TowardPi swept-source optical coherence tomography (SS-OCT) and OCT angiography (SS-OCTA) enable ultra-high resolution, enhanced penetration with longer wavelength (1060 nm), a rapid scan rate (400 KHz), reduced loss of signal strength with increasing depth, and 120\({}^{\circ}\) angular widefield of fundus view, enabling a nearly histological description of the retina and choroid. We therefore used this SS-OCT and SS-OCTA platform to observe the intrinsic features of osteoma in 23 eyes of 21 patients. It was found that the borders of CO were clearly demarcated from the adjacent choroidal Sattler's and Haller's layers, while on a corresponding B-scan the blood flow of the CO was detected mainly within the choriocapillaries and partly within Sattler's layer. The CNV was identified as numerous branching or radiating vessels connecting with intrinsic feeder vessels displaying various patterns including ginseng, instant noodle, growth ring, tangle, spider web, medusa, seafan, and irregular shape. Moreover, tumor-like tissues were found to grow above the disrupted Bruch's membrane. SS-OCTA can be used to detect the tumor vasculature in CO.  
choroidal osteoma; swept-source OCT; OCTA; tumor vasculature; neovascularization Article  
Clinical Observation of Choroidal Osteoma Using Swept-Source Optical Coherence Tomography  
may not be clearly visualized, and are commonly difficult to distinguish from CNV via traditional FA and ICGA, thus leading to improper management [5]. Multimodal imaging approaches including optical coherence tomography (OCT) and OCT angiography (OCTA) can reveal the chorioretinal features of CO [6; 7; 8; 9; 10], but the resolution and depth of penetration of these modalities have been insufficient to reveal the tumor histology. By altering the imaging acquisition techniques of spectral-domain OCT (SD-OCT), such as enhanced depth imaging (EDI), it is possible to obtain deeper and unique intrinsic bone features suggestive of bone lamellae, cement lines, Haversian canals, Volkmann canals, and trabeculae, yielding a level of detail comparable to histopathology [11; 12; 13; 14]. Swept-source OCT (SS-OCT) has the benefits of ultra-high resolution (3 \(\upmu\)m), high penetration as a result of long wavelength (1040-1050 nm), rapid scan rate, and reduced loss of signal strength with increasing depth, thereby providing subtle imaging characteristics of choroidal pathologies on a par with histological sections and superior to SD-OCTA images (approximately 840 nm). Building on the principle of OCT, SS-OCT has also been applied to SS-OCTA, thus enabling non-invasive depth-resolved imaging of the retinal and choroidal microvasculature [15]. Despite the advantages of SS-OCT and SS-OCTA, they are seldom used in the imaging of CO [16; 17]. The recently developed TowardPi full range SS-OCT and SS-OCTA system has an A-scan rate of 400 KHz (BMizar) and a wavelength centered at 1060 nm, resulting in deeper penetration and lower scattering at the retinal pigment epithelium (RPE). Furthermore, the BMizar system has an inbuilt lens that acquires data from an area of 24 mm in width (120\({}^{\circ}\) angular field of fundus view) while retaining the same resolution as from smaller scan sizes. This can provide imaging of an entire tumor with a single capture. Moreover, the inexpensive TowardPi data acquisition card (DAQ) runs at 6 GB/s and 12 bits, with a signal-to-noise ratio (SNR) of 56 dB, which is well-matched to the 400 KHz laser source. The scan rate is almost twice that of SD-OCT devices, allowing shorter acquisition times and potentially reducing imaging artifacts. In addition, TowardPi has developed a three-dimensional spatial identification algorithm to visualize all layers of choroidal vessels.