Updated 8/6/2008 – summary of paper published by Shields et al. Ophthalmology 2008.
These are benign pigmented lesions of the layer behind the retina known as the choroid are found in 6.5% of patients over the age of 49. Although they can be found in patients less than 20 years of age, their frequency increases with age. About 10% of choroidal naevi are non-pigmented. They need to be distinguished from choroidal melanoma, pigmented choroidal metastases, subretinal or choroidal haemorrhages and retinal pigment epithelial tumours. The differential diagnosis of non-pigmented choroidal naevi include amelanotic melanoma, chroidal metastasis, choroidal haemoangioma, choroidal granuloma, choroidal osteoma and posterior scleritis.
Visual loss is rare for extrafoveolar choroidal naevi, but may occur in about 25% of patients when situated beneath the fovea. The causes of visual loss in these patients is caused by the accumulation of subretinal fluid, retinal pigment epithelial detachment and foveal oedema. Subretinal fluid (SRF) overlying or adjacent to choroidal naevi is found in about 10% of cases. SRF is a risk factor (relative risk 1.6) for the development of malignant melanoma and is deemed to be particularly significant when associated with preservation of outer retinal layers and photoreceptors (atrophy and retinal thinning imply chronicity – a benign feature)
About 1 in 8845 naevi transform into malignant melanoma in the Caucasian population (Singh eg al Ohthalmology 2005). Risk factors for the development of melanoma include thickness over 2 mm, SRF, symptoms, orange pigment, location near the optic disc and lack of overlying drusen.
The need for follow-up of patients with choroidal naevi is debatable. In one study of patients over 49, only 1 in 160 showed growth on follow-up (Thiagalingam et al. Archives of Ophthalmology 2004), but in another, naevus growth was seen in 14% of young patients, 9% of middle-age and 6% of older patients (Shields et al. Ophthalmology 2008).