Subclinical subretinal fluid detectable only by optical coherence tomography in choroidal naevi—the SON study

Background: Subretinal fluid is a risk factor for growth and malignant transformation of choroidal naevi, however it is unclear if this applies to subclinical fluid that is only detectable by optical coherence tomography (OCT). The objective of this study was to determine the prevalence and associations of subclinical but OCT-detectable subretinal fluid over choroidal naevi. Methods: Cross-sectional study of 309 consecutive cases of choroidal naevi imaged by OCT between July 2017 to January 2019. Multicentre international study involving ten retinal specialist centres. All patients presenting to retinal specialists had routine clinical examination and OCT imaging. The prevalence of subclinical OCT-detectable subretinal fluid over choroidal naevi and its associations with other features known to predict growth and malignant transformation were noted and analysed. Results: Of 309 identified consecutive cases, the mean patient age was 65 years, 89.3% of patients were Caucasian and 3.9% were Asian. The prevalence of subclinical but OCT-detectable subretinal fluid associated with choroidal naevi was 11.7% (36/309). Naevi with fluid were associated with larger basal diameters, greater thickness, presence of a halo, orange pigmentation, hyperautofluorescence, and hypodensity on B-scan ultrasonography. Conclusion and relevance: Of choroidal naevi where subretinal fluid is not visible on clinical examination, 11.7% demonstrate subretinal fluid on OCT scans. These naevi more commonly exhibit features known to be associated with growth and transformation to melanoma. The presence of subclinical OCT-detectable fluid over choroidal naevi may assist in their risk stratification.