What You Should Know About Eye 'Freckles'
Some people notice small dark spots that look like freckles in the iris of the eye. These may be harmless iris "freckles," medically called iris ephelis. Occurring in about 60 percent of people, these flecks on the surface of the iris (the colored part of the eye) are due to increased amounts of the pigment melanin produced by cells called melanocytes. They do not affect your vision and do not develop into malignant melanoma.
Until recently, little was known about the origin of iris freckles, but a 2017 study in Investigative Ophthalmology & Visual Science, which included 632 people in Austria, linked them to several factors, including lifetime number of sunburns, history of severe sunburns (that cause blisters), sun-damaged skin, increasing age, and light-colored eyes. Interestingly, the freckles were found to be more common in the lower outer part of the iris (farther away from the nose), possibly because that part of the eye isn't well protected from the sun by the shade cast from the nose or eyebrows, the researchers speculated. The researchers concluded that the presence of iris freckles is an "easily accessible" potential marker for chronic sun exposure and that evaluating them "could be helpful in understanding the role of sunlight in several ophthalmologic diseases."
Dark spots that are visible on the iris could also be iris nevi, however, which infiltrate the stroma (a layer of the iris), are larger than iris freckles, and grow larger with time. These benign spots are due to an increase in the number of melanocytes, rather than just an increase in the amount of melanin within melanocytes, as occurs in iris freckles. Their exact prevalence isn't known, but it's thought that they affect only about 4 to 6 percent of adults, more commonly in those with light-colored eyes and with increasing age. Some iris nevi are congenital, formed during the embryonic development of the eye. As with iris freckles, iris nevi don't cause any symptoms, though in a very few cases they grow rapidly, leading to eye problems, such as glaucoma. Only in very rare cases do iris nevi become malignant.
Both iris freckles and nevi can be seen with the naked eye, but an eye exam can distinguish between the two. Choroidal nevi, another kind of eye "freckle"—found inside the eye, in the layer just beneath the retina—can be seen only during an eye exam. If your eye doctor spots one of these, you should be monitored regularly, since these have a higher chance of evolving into melanoma compared to iris nevi (though the risk is still slight—about one in 500 over 10 years).