Your ophthalmologist has told you that you have a freckle in 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 not a serious problem. Both need to be monitored to make sure they are not malignant melanomas.
Congenital hypertrophy of the retinal pigment 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 increased pigment in the cells of the retinal pigment epithelial cell layer. This is hypertrophy, or an increase in the size but not the number of cells. The blood vessels below him also atrophy, resulting in a small blind spot that he is unable to perceive. While there are often changes over time; it is above all a stable and inconsequential change, and congenital hypertrophy of the retinal pigment epithelium can be thought of 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 can change from a normally flat surface to develop raised nodules. The formation of these tumors is very rare, but is checked annually by ophthalmologists. No further tests other than dilated eye exams are usually required 3 to 6 months after the first observation, and yearly thereafter.
Congenital hypertrophy of the retinal pigment epithelium also occurs in a form called “bear tracks.” Bear tracks are multiple dark spots at 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 to detect colon and rectal cancer. This may be due to a dominant gene that often runs 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 have colon cancer, but it is more likely if they are large, are present in both eyes, and there are more than 3 or 4 spots in each eye. Isolated single congenital hypertrophy of retinal pigment epithelial spots is not associated with familial polyps or with an 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 pigmented epithelium, but they are irregular in shape. They are due to a real increase in the number of cells of the retinal pigment epithelium. The main concern in this case is to monitor the condition that caused it. If it is an infection in one of the layers of the eye it could reappear at a later date.
A choroidal nevus is actually like a nevus (freckle) but it occurs on the choroid, the level below the retina that supplies circulation to the retinal tissue. These appear as round, gray, 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 rather pigmented epithelial cells. A choroidal nevus is usually flat, but appears more similar to melanomas in the choroid because it sits 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.
Tests to diagnose any new spots seen 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 eye exam is the only technique that allows ophthalmologists to adequately detect most of these spots. Although this may be slightly uncomfortable and cause light sensitivity and mild dry eyes, it should be done by your optometrist. Patients often have not routinely had their eyes dilated in the past, so when your optometrist finds a new spot or freckle in your eye, it may have been 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 to detect any changes. In areas with high amounts of UV exposure, such as northern Colorado, UV-protective sun clothing can 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, use of the sun and moderate UV exposure may become the recommendation.