What Causes Eye Color?

One of the most striking features of a person’s appearance is the color of their eyes. But what gives color to a person’s eyes, and can they change over time? Take a look to find out!

What Determines Eye Color?

There are actually several factors that influence an individual’s eye color, but as babies, most people actually have blue eyes. This is because melanin—a natural pigment that occurs in the iris and other parts of the body—is not fully present by the time by the time a child is born, and as a result, most babies’ eyes appear blue. As the child gets older, his or her eyes will begin to produce melanin, and the quantity of melanin as well as its location within the various layers of the iris determine what eye color they will grow to have because of how visible light reflects off of melanin in the eyes.

For example, people with blue eyes have melanin in the back layers of the iris but not the front; people with brown eyes have a large presence of melanin in the front layers of the iris; people with green or hazel eyes fall more melanin than blue-eyed people but less than brown-eyed people.

Will a Child Have the Same Eye Color as Their Parent?

Not necessarily. Parents pass on genes to their children, and there are many genes that affect eye color, especially the OCA2 gene on Chromosome 15. The OCA2 gene produces a protein that helps to produce and release melanin within the eyes. Since there are multiple variants of the gene and these variants determine how much or how little melanin is produced in the eyes, it’s really a person’s genes that are the greatest influence on their eye color. So while parents pass on chromosomes to their children that determine eye color, children may actually have the same or different colored eyes as their parents.

Can Eye Color Change?

10-15% of Caucasian people, who generally have lighter eye colors, may experience changes in their eye color. This isn’t limited to just blue or lighter colored eyes, however: Hazel eyes can get even darker, for example. If your eye color as an adult changes significantly or if one of your eyes changes from blue or green to brown—known as heterochromia—you should consult your eye doctor to make sure that it is benign and not the result of diseases like Horner’s syndrome, pigmentary glaucoma, or others.

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