Features of choroidal naevi on swept source optical coherence tomography angiography and structural reverse flow optical coherence tomography

Abstract

The purpose of our study was to describe features of choroidal naevi as seen on swept source optical coherence tomography angiography (OCTA) and also on en face images derived from structural data from OCTA. A prospective observational cohort study was carried out. Patients attending a specialised choroidal naevomelanocytic with known naevi were imaged with swept source OCTA. Seventy-one eyes of 70 patients were imaged. Forty-three patients and 44 eyes were included. Mean age was 57.7years (SD 14.9), range 29-81years. Male to female ratio was 20:23. On OCTA after manual segmentation, naevi could be seen in 47.6% of cases, whereas in the en face images, naevi could be clearly visualised in 79.5% of cases. In OCTA, the superficial and deep capillary plexuses appeared undisturbed as did the outer retinal layer appeared in all cases of flat naevi. In choroidal naevi with mild elevation, the outer retinal layer appeared more susceptible to projection artefacts from overlying retinal vasculature. The choriocapillaris layer showed a fading of the normal homogenous vascular mosaic corresponding to the area of the naevus. In the en face images, even the faintest and thinnest naevi could be visualised in striking detail, and naevi greater than 120μm thickness appeared darker (p = 0.0034). OCTA presents characteristic changes in the choriocapillaris layers in cases of choroidal naevi. The association of naevus substance appearing darker with increasing thickness may offer a novel prognostic clue. En face structural OCT may allow accurate, detailed measurement of lateral dimensions which could be of value in the monitoring of suspicious naevi.