What is a choroidal nevus?
Nevus is a Latin word that means birthmark. In medical terminology it also refers to moles. The plural of nevus is nevi, and nevi can appear on your skin, the surface of the eye or inside the eye.
A nevus inside the eye is called a choroidal nevus because it is found in the tissue of the eye called the choroid. The choroid is under the retina. The choroid is a sponge-like membrane with many blood vessels and it supplies nutrients to the retina. Choroidal nevi are common and occur in about 10% of adults.
A nevus is formed from pigment cells, which are called melanocytes. These are the same type of cells that give hair, skin, and eyes their color.
A nevus in the eye is often called an eye freckle. They can be found in three different areas of the eye—the white of the eye (conjunctiva), the iris (colored part of the eye), and inside the eye in the choroid layer.
No matter where they are found within the eye, they are mostly harmless, will not affect your vision, and do not require any treatment.
What Causes Eye Nevi?
No one really knows what causes them, but it has been thought that ultraviolet light may play a role in their development because there is a higher incidence of nevi in people with blue eyes and people who work outdoors. For that reason, wearing sunglasses to protect your eyes from ultraviolet light is always a good idea. Nevi are also more common in people with light skin tones.
Nevi that Require Treatment
A very small percentage, about 2 to 5%, of nevi require special attention.
Choroidal nevi that require additional monitoring and testing are large or thick nevi, those with an orange pigment, or ones that are leaking fluid.
Nevi with these characteristics are more likely to grow into a choroidal melanoma and for that reason must be carefully monitored and should be examined with an ultrasound scan and possibly a fluorescein angiography.