What's the Risk of Melanoma with a Choroidal Nevus?

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Atypical Choroidal Nevus by eyedolatry
This patient has perfect 20/20 vision, and has been assessed for several years
by ocular oncologists and believed to NOT have ocular melanoma but just a
suspicious nevus at this time.
If you have a freckle inside your eye (or choroidal nevus in its technical term), your doctor has talked with you about the need to monitor its appearance.  Choroidal nevi are present in around 5-8% of the Caucasian population, and do not cause any changes to vision since they are present in the tissue underlying the retinal cells.  That means that you will not know if you have one unless you are getting routine dilated eye examinations or retinal photography!  Eye exams are essential for those with normal vision too.

Unlike choroidal nevi, choroidal melanoma are exceedingly rare--present at a rate of around 6 per 1 million individuals.   The overwhelming majority of choroidal nevi will never become a melanoma.--only about one in over 8,000 nevi have a malignant transformation.  At every eye exam, your doctor will assess your nevus for malignant suspicion, ruling out any potential risks or referring you to a specialist if further investigation is necessary.  Since both nevi and early melanomas typically have no associated pain or vision loss, the best way to determine your risk is to have your doctor look with dilation or retinal photography for suspicious characteristics.  How does your doctor determine risk? Here are the key factors we look for:
A confirmed ocular melanoma with autofluorescence of lipofuscin (as seen on right) and peripapillary position. via

To Find Small Ocular Melanoma  (Mnemonic and information credited to Dr. Carol Shields)

Thickness: suspect melanoma if the thickness is > 2 mm

  • The only true way to assess thickness is to run an B scan ultrasound of the area in question.  Your doctor will typically try to determine based on vessel bend if the lesion is flat or elevated.  If elevation is expected, then they will likely refer you for a ultrasound to determine the exact amount of thickening
Sub-retinal Fluid: Fluid or edema around the area of the lesion is a sign that the growth is pushing or disrupting the overlying retinal layers -- a clear sign of possible malignant transformation.  OCT imaging can be used to detect edema around the lesion.

Symptoms: Flashes, floaters, or significant vision changes are always symptoms hat should be investigated.  Typically these visual symptoms are not the result of the melanoma, but are associated with edema or serous retinal detachments that are the result of a melanoma's growth. 

Orange Pigment: Lipofuscin is pigment granules that are produced by lysozomal digestion at the cellular level.  They are an indicator that your lesion has active metabolism, which implies a growing lesion!  Lipofuscin appears as bright orange pigmentation around the edge of the lesion or will hyperfluoresce with fundus autofluorescent cameras.  The photo above is a good example of the orange pigmentation we will often see with lipofuscin.

Margin Touching the Optic Nerve: If your nevus is by the nerve, the associated risk if much larger.  The optic nerve is a highway directly from the eye to the brain, so a melanoma in this area is also much riskier for metastasis.

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