Your ophthalmologist has told you that you have a freckle on your eye. Should you be worried? It could be a number of things, but most likely a choroidal nevus or benign choroidal melanoma with congenital hypertrophy of the retinal pigment epithelium. Both conditions are usually benign and do not constitute a serious problem. Both need to be monitored to make sure they are not malignant melanomas.
Congenital hypertrophy of the retinal pigmented epithelium (also known as a halo nevus) is a well-demarcated, dark pigmented spot within the back of the eye on the retina. Although the size varies, it’s convenient to think of it as equivalent to the top of an eraser on a pencil. It is an accumulation of pigment increases in the cells of the cell layer of the retinal pigment epithelium. This is hypertrophy, or an increase in the size but not the number of cells. The blood vessels under him also atrophy, resulting in a small blind spot that he is unable to perceive. While there are often changes over time; it is mostly a stable change without consequences, and congenital hypertrophy of the retinal pigment epithelium can be considered as a freckle on the skin. The difference is that you can’t see any changes like you can with a spot on your hand, so serious conditions can progress beyond the treatable stages. Rarely, a halo nevus may change from a normally flat surface to develop raised nodules. The formation of these tumors is very rare, but is checked annually by ophthalmologists. Testing other than dilated eye exams is usually not required 3 to 6 months after first observation, and annually thereafter.
Congenital hypertrophy of the retinal pigment epithelium also presents in a form called “bear tracks.” Bear tracks are multiple dark spots on the back of the eye that look like small bear tracks. They often occur along with a condition called familial polyps and require further testing for colon and rectal cancer. This may be due to a dominant gene that is often seen in families as a predisposition to colon cancer. Bear Tracks can be seen years before cancer occurs, so they can be a valuable preventative sign for your optometrist. Bear tracks may require a referral to another specialist for further evaluation. Not all patients with Bear Tracks will get colon cancer, but it is more likely if they are large, present in both eyes, and there are more than 3-4 spots in each eye. Isolated single congenital hypertrophy of retinal pigment epithelial spots is not associated with familial polyps or with increased risk of colon cancer.
Trauma to the retina, either from injury or infection in the eye, can cause dark spots similar to congenital hypertrophy of the retinal pigment epithelium, but are irregular in shape. They are due to an actual increase in the number of retinal pigment epithelium cells. The main concern in this case is monitoring the condition that caused it. If it is an infection in one of the layers of the eye it could recur at a later date.
A choroidal nevus is actually like a nevus (freckle) but occurs in the choroid, the level below the retina that supplies circulation to the retinal tissue. These appear as round, grey, usually flat spots and are very common in up to 30% of the population. They are also known as benign choroidal melanomas, although they are not true melanomas. They are due to an increase in pigment cells in the choroid. These types of cells are found in our skin and in parts of the eye. The retina does not have the same type of pigment cells, but pigment epithelial cells. A choroidal nevus is usually flat, but appears more similar to melanomas on the choroid because it lies at the same level below the retina. They require closer observation and sometimes further testing to make sure they are benign spots. Any nevus can undergo a transformation to melanoma but it is very rare.
Testing to diagnose any new spots observed may include continuous observation, optical coherence tomography techniques to image the layers of the retina, digital imaging, and dye imaging of the retina. An annual dilated examination of the inside of the eye is the only technique that allows ophthalmologists to adequately detect most of these spots. Although this can be slightly uncomfortable and cause light sensitivity and mild dry eyes, it should be done by your optometrist. Often, patients have not had their eyes routinely dilated in the past, so when your optometrist finds a new blemish or freckle in your eye, it may have remained there unchanged for years. You can rest easy knowing that the vast majority of the time it is completely harmless and only needs to be rechecked once a year for any changes. In areas with high amounts of UV exposure, such as northern Colorado, UV-protective sunwear may help reduce the risk of melanomas. There is some controversy about UV exposure and cancer, and some suggestions that vitamin D may reduce certain types of tumors and colon cancer associated with bear tracks. In the future, sun use and moderate UV exposure could become the recommendation.