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

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.

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.

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.

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.