Ultra-wide-field imaging assessment of small choroidal pigmented lesions using red and green colour channels

Background: Diagnosis of small choroidal melanoma is mainly based on tumour thickness, subretinal fluid, or lipofuscin pigment. Ultra-wide-field imaging (UWF) allows depiction of choroidal lesions through a red (RC) and a green channel (GC). Aim of the study was to determine the utility of this tool in the detection of small choroidal melanoma. / Methods: Retrospective cross-sectional study of patients with small choroidal pigmented lesions up to 3 mm in thickness. All patients underwent clinical and imaging assessment including UWF. Lesions were subcategorized based on thickness and lesion type. A qualitative assessment ensued using the red and green channels feature. / Results: A total of 152 patients were included. Melanotic naevi (76/152,50%) and small choroidal melanomas (55/152,36%) were the predominant types. Thickness was <1 mm in 30% (46/152), 1–2 mm in 46% (70/152) and 2–3 mm in 24% (36/152) of cases. Two distinct imaging patterns were noted: dark on RC/undetectable on GC and dark on RC/light on GC. In melanotic naevi the dark on RC/light on GC pattern was significantly associated with increased tumour thickness (p = 0.006) and the presence of lipofuscin (p < 0.001) suggesting a potential prognostic significance. In small melanomas such an association was not established. The majority of small melanomas manifested a dark on RC/undetectable on GC pattern despite the presence of subretinal fluid and lipofuscin. / Conclusions: UWF imaging of choroidal pigmented tumours with red–green channels revealed two distinct patterns. The dark on RC/light on GC pattern was more common in suspicious melanotic naevi, but not in small melanomas. The use of red–green channels is not a reliable diagnostic tool in the early detection of small melanomas