Choroidal nevi

Choroidal nevi are a benign proliferation of melanosities in the normally pigmented choroid. Because they are beneath the pigmented RPE, they often appear slate gray with feathery borders and can be completely hidden by a well-pigmented RPE when viewed with the visible light (but remain visible in the infrared). Most choroidal nevi are 5 mm or less in diameter and 1 mm or less in thickness, but they can attain a diameter of 10 mm or more, and a thickness of 3 mm or more (for reference, the average optic nerve in Caucasians is 1.5 mm in diameter). Drusen, seen as small, yellow-white inclusions in the overlying RPE, can be taken as a sign that the nevus is long-standing and, by extrapolation, absent malignant growth. (Contributed by Dr. James Walters.)