So you have been told by your eye doctor there is a freckle in your eye. Should you be worried? It could be a number of things but the most likely are choroidal nevus (benign choroidal melanoma) or CHRPE (congenital hypertrophy of the retinal pigmented epithelium). Both conditions are usually benign and not a serious problem. They both need to be monitored to make sure they are not malignant melanomas.
Congenital hypertrophy of the retinal pigmented epithelium (also known as halo nevus) is a pigmented, well demarcated dark spot inside the back of your eye on your retina. Though size varies, it is convenient to think of it as about equivalent to the top of an eraser on a pencil. It is an accumulation of increases in pigment in the cells of the retinal pigment epithelium cell layer. This is hypertrophy, or an increase in the size but not the number of cells. The blood vessels underneath it atrophy also which results in a small blind spot which you are not capable of perceiving. While there are often changes over time; it is mostly a stable, inconsequential change and CHRPE can be thought of like a freckle on your skin. The difference is you can’t observe it for any changes like you can a spot on your hand, so serious conditions can advance past the treatable stages. On rare occasions a halo nevus can change from a normally flat surface and develop elevated nodules. The formation of these adenoma tumors are very rare but something eye doctors do check for on an annual basis. Usually no further tests are required other than eye exams with your eyes dilated in 3-6 months after first observation, then annually there after.
CHRPE also occurs in a form called “Bear Tracks.” Bear tracks are multiple dark spots in the back of the eye that look like little bear footprints. They frequently occur in conjunction with a condition called familial adenomatous polyposis and require further testing for colon and rectal cancer. This can be due to a dominant gene that is often seen to run in families as an predisposition to colon cancer. Bear Tracks may be seen years before the cancer occurs so they may be a valuable preventative sign to your optometrist. Bear tracks may require a referral to a Gastroenterologist Doctor for further evaluation. Not every patient 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 or 4 spots in each eye. Isolated single CHRPE spots are not associated with Familial adenomatous polyposis or an increased risk of colon cancer.
Trauma to the retina whether from injury or infections in the eye can cause dark spots similar to CHRPE but they are irregular in shape. They are due to an actual increase in the number of retinal pigment epithelial cells which is called hyperplasia. The primary 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 recur at a later date.
A choroidal nevus is indeed like a nevus (freckle) but it is occurring in the choroid, the level below the retina which supplies circulation to the retinal tissue. These appear as round, grey, usually flat spots and are very common occurring in up to 30% of the population. They are also referred to as benign choroidal melanomas, though they are not true melanomas. They are due to an increase of melanocytes in the choroid. Melanocytes are the cells that hold pigment. They are found in our skin and in parts of the eye. The retina does not have melanocytes, it has pigmented epithelium cells instead. A choroidal nevus is usually flat, but does appear more similar to melanomas in the choroid due to being located 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 transformation to a melanoma but it is very rare.
Testing to diagnose any new spot observed can include ongoing observation, optical coherence tomography techniques of imaging the layers of the retina, digital imaging pictures, and fluorescein angiography of the ocular fundus. A dilated exam of the inside of your eye (fundus) annually is the only technique that allows eye doctors to adequately detect most of theses spots. Although this can be mildly uncomfortable causing light sensitivity and mild dry eyes, it should be done by you optometrist. Frequently patients have not had their eyes routinely 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 be reassured in knowing that the large majority of the time it is completely innocuous and only needs to be rechecked once every year for any changes. In areas with large amounts of UV exposure like Northern Colorado, sunwear with UV protection can help reduce the risk of melanomas. There is some controversy over UV exposure and cancer, and some suggestions that vitamin D may reduce certain type of cancer such as adenomas and the colon cancer seen associated with bear tracks. In the future, sunwear and moderate exposure to UV could become the recommendation.