What is a choroidal nevus?
A nevus is a commonly occurring growth composed of a cluster of cells called melanocytes, the cells that make the pigment in skin, hair, and eyes. Nevi (the plural of nevus) can develop under the retina, the specialized nerve tissue lining the back of the eye that detects light and color. Behind the retina is the choroid, a layer of blood vessels that bring oxygen and nutrients to the eye. Nevi that develop in this layer are choroidal nevi. These are usually harmless, but should be monitored regularly because they have the potential to evolve into an aggressive cancer called melanoma.
In the US 10-13% of adults have choroidal nevi. (Choroidal nevi are not typically observed in young children.) The chances of a nevus transforming into a malignancy are low (one in 500 choroidal nevi will undergo a transformation into a melanoma if monitored for 10 years). When examined with an opthalmoscope most choroidal nevi appear gray, brown, yellow, or a combination of colors. Nevi that are orange, thicker than normal, or that leak fluid have a higher likelihood of becoming malignant.
How is a choroidal nevus diagnosed?
Ophthalmologists often discover a nevus during a routine eye exam. The ophthalmologist will take a picture of the nevus to track any changes in its appearance from visit to visit. If the nevus has the characteristics noted above they may follow up the initial observation with additional tests such as
- Ultrasound: An imaging test in which high-energy sound waves (ultrasound), are bounced off the internal tissues of the eye, to create an image of the inside of the eye.
- Fluorescein angiography: A examination of the blood vessels and the flow of blood inside the eye.
- Ocular coherence tomography: An imaging test that uses light waves to detect swelling or fluid beneath the retina.
How is a choroidal nevus treated?
Most choroidal nevi do not require treatment, but ophthalmologists will photograph them at each visit and compare the new image to any previous ones. changes in the size or shape of a nevus suggest that it should be examined more closely. In rare cases, a nevus on the outer wall of the eye that is affecting the eye’s appearance may be removed with surgery.