Most eyes are blue, green or brown in color. Infants are born with blue or dark eyes but the color may change until children are about 9 months old, or sometimes up until a child reaches the age of 3. After that, eye color change may be caused by disease or other medical reasons, according to the University of Maryland Medical Center.
Significance
The iris is the muscle in the eye that controls the pupil. Eye color is determined by the amount of pigment in the iris. Allaboutvision.com notes that eye color is genetic and the most common eye colors are green, blue and brown, but science does not yet fully understand how colors such as gray, hazel and other combinations form.
Development and Eye Color Change
As babies grow, eye color becomes deeper. The change usually happens because melanin, a brown pigment not present initially, grows with age and makes the eyes darker. This is usually complete by the age of 3.
Ocular albinism, a less common form of albinism than oculocutaneous albinism that involves the hair and skin, primarily affects the eyes. People born with albinism can have different-colored eyes, including blue or brown, or the eyes may appear to be pink or red.
Disease
Glaucoma causes the eye to appear lighter or cloudy. Other illnesses affecting eye pigmentation are rare but do occur, according to a study published in the U.S. Library of Medicine. Melanin pigment differences are seen in conditions such as Fuchs' crypts and Wolfflin nodules, and have also been noted in Horner Syndrome, a rare condition of damaged nerves that affects the eyes and face and causes the iris to lack color.
Medications
Some glaucoma medications affect the cells in the iris and cause the eyes to darken. Dr. Robert D. Newcomb, O.D., professor of clinical optometry at Ohio State University, notes this is more of a problem for patients with blue and green eyes, but rarely for those with brown eyes.
Considerations
It is possible to have two different-colored eyes. Heterochromia or heterochromia iridium is usually caused by heredity and is more common in dogs and rare in people, but does happen. Famous people who have heterchromia include David Bowie, Dan Aykroyd and Jay Crawford, sportscaster and morning host for ESPN's "First Take."
