high-risk tumors now allows early detection, when melanomas are small and life prognosis is better [6–12]. Through the years, there has also been constant evolution in ocular imaging in parallel with improved treatment outcomes, globe salvage, and visual outcomes. These ancillary tests help clinicians identify melanomas earlier and manage treatment complications, ranging from ultrasonography, intravenous fluorescein angiography (IVFA), indocyanine green angiography (ICGA), to optical coherence tomography (OCT) [12–27]. Today, this process of evolution has taken us to non-invasive, dyeless, high-resolution angiography using OCT technology in the form of OCT angiography (OCTA) [28, 29].
Here, we review the use of OCTA in the evaluation of choroidal melanoma, particularly its role in differentiating melanomas and pseudomelanomas, in addition to discussing its utility in the early detection and management of radiation retinopathy. Lastly, we deliberate the current limitations of OCTA technology and future developments that could be relevant in ocular oncology.
Clinical and Traditional Imaging Features of Uveal Melanoma
The majority of human melanomas are found in the skin (91%), followed by the eye (5%) and mucosa (1%) [30]. In the eye, most are located along the uveal tract, involving the iris (3.5%), ciliary body (6.1%), and more frequently, the choroid (90.3%) [31]. It typically occurs in older Caucasian males, with an average age at presentation of 58–60 years [5, 32]. Clinically, choroidal melanomas are often pigmented, dome-shaped tumors that have overlying subretinal fluid and orange pigment [1, 6–12, 31]. Other less common features include extraocular extension, retinal invasion, vitreous hemorrhage, and Bruch’s rupture that gives tumors a bi-lobed or mushroom-shaped configuration as it herniates through the break in Bruch’s membrane [5, 11, 31]. The prognosis of choroidal melanoma is vastly dependent on tumor size at presentation, as it was consistently predictive of systemic metastasis in large single-center cohorts, multi-center trials such as the Collaborative Ocular Melanoma Study (COMS), and has been incorporated into the American Joint Committee on Cancer (AJCC) staging of uveal melanoma [2–5].
Ocular imaging is critical in the management of choroidal melanoma. Ultrasonography typically shows an echolucent dome-shaped mass with choroidal excavation, vascular pulsations, and subretinal fluid [13, 14]. It also allows the measurement of tumor size, having less limitation than OCT for large tumors given its greater scan depth, but tends to overestimate tumor dimensions compared to OCT for small melanomas [26]. IVFA and ICGA can show intratumoral vessels, and when superimposed on the overlying normal retinal vessels reveals the classic “double circulation” [15–17]. However, this feature is not always present, and is seen mostly when Bruch’s rupture and retinal invasion are present, as the intratumoral vessels are masked by the retinal pigment epithelium (RPE) when it is still confined within the choroid [17]. Purely choroidal melanomas show patchy or lacy hyperfluorescence/hypercyanescence without a specific fluorescent/cyanescent pattern by IVFA or ICGA, respectively [15–17]. Fundus autofluorescence provides insights into the overall health of RPE and permits greater visualization of orange pigment in choroidal melanoma [19, 20]. OCT, on the other hand, improves the detection of subretinal fluid compared to clinical examination, and consequently provides insight into systemic prognosis, as subretinal fluid is a known risk factor for systemic metastasis [5, 19, 20]. Even if subretinal fluid is seen with choroidal nevi, Espinoza et al. [22] described an active pattern of subretinal fluid in choroidal melanomas, wherein fluid accumulates under retinal tissue with normal thickness, in contrast to a chronic pattern in choroidal nevi, when fluid accumulates under thinned retina and thickened RPE. Using enhanced depth imaging OCT (EDI-OCT) to provide better resolution of the choroid, Shields et al. [24] imaged 37 small (≤3 mm) choroidal melanomas. They reported posterior shadowing (97%) and compression of choriocapillaries (100%) in almost all tumors [24]. More importantly, the presence of shaggy photoreceptors (49 vs. 0%, p < 001), loss of ellipsoid line (65 vs. 6%, p = 0.02), loss of external limiting membrane (43 vs. 2%, p = 0.008), and overlying intraretinal edema (16 vs. 0%, p = 0.003) were features more strongly associated with choroidal melanoma than nevi [24]. Mashayekhi et al. [33] also found a remote subclinical macular edema (central macular thickness [CMT] >10 μm compared to the fellow eye) in 54% of eyes with choroidal melanoma, and even showed subclinical macular edema to be predictive of future cystoid macular edema (CME). Furthermore, subclinical macular edema was associated with larger tumors (diameter and thickness), as well as subretinal fluid [33]. Irrespective of the constellation of known clinical and imaging features of choroidal melanomas, there is no single pathognomonic sign. Hence, accurate diagnosis may require consolidation of findings obtained through history, clinical evaluation, and appropriate imaging.
OCTA Features of Choroidal Melanoma
OCTA is a non-invasive means to perform high-resolution dyeless angiography [29]. Through segmentation of OCT B-scans, OCTA also provides a layer-by-layer analysis of the retinal vasculature [28, 29]. Unlike IVFA, which only visualizes the major arterioles, major venules, and the superficial capillary network, OCTA also allows analysis of the deep capillary plexus and the radial peripapillary capillaries (RPC) in vivo, which were previously not possible [29]. Using OCTA, new metrics to describe