A person’s eye color results from pigmentation of a structure called the iris, which surrounds the pupil and helps control how much light can enter the eye. The color of the iris ranges on a continuum from very light blue to dark brown. Most of the time eye color is categorized as blue, green/hazel, or brown. Brown is the most frequent eye color worldwide. Lighter eye colors, such as blue and green, are found almost exclusively among people of European ancestry.
Eye color is determined by variations in a person’s genes. Most of the genes associated with eye color are involved in the production, transport, or storage of a pigment called melanin. Eye color is directly related to the amount and quality of melanin in the front layers of the iris. People with brown eyes have a large amount of melanin in the iris, while people with blue eyes have much less of this pigment.
Most babies are born with blue eyes that can darken in their first three years. Darkening occurs if melanin develops with age. Children can have completely different eye colors than either of their parents. But if both parents have brown eyes, it's most likely that their children also will have brown eyes. The darker colors tend to dominate, so brown tends to win out over green, and green tends to win out over blue.
Eye color also can change with age. This happens in 10 to 15 percent of the Caucasian population. If your adult eye color changes pretty dramatically, or if one eye changes from brown to green or blue to brown (called heterochromia), it's important to schedule a comprehensive eye exam with your eye doctor. Eye color changes can be a warning sign of certain diseases that may need immediate attention.
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