What Determines Eye Color?

One of the most fascinating genetic traits in people is eye color. The most common colors are blue, brown and green. In addition, there is quite a variation in each of the three main colors, plus other colors, such as gray and hazel. Eye color can even change as people age.

  1. Genes Play a Role

    • A common theory for eye color used to be that brown eyes are "dominant" and blue is "recessive." Experts have concluded that it is not that simple. Scientists now say multiple genes are involved in determining eye color. The biggest effect is the OCA2 gene, according to University of Queensland geneticist Rick Sturm, because this particular gene controls the amount of melanin (or pigment) produced. Each parent contributes two pairs of genes on each chromosome, so the eye color of the child has multiple possibilities. In fact, the baby can have a totally different eye color than either parent.

    Age Plays a Role

    • Many babies are born with blue eyes that tend to be darker by the time they are 3 years old. According to Burt Dubow, OD, at All About Vision, 10 to 15 percent of the Caucasian population (people who generally have lighter eye colors) experience a change in eye color as they age. Dramatic changes in color, however, could be a warning sign of disease, so it is important to see an eye doctor if this occurs.

    What Is Your Mood?

    • Perhaps someone has told you that your eyes change color when you are angry. The iris (the part of the eye with pigment that determines the color) expands and contracts to control pupil size, so when the pupil size changes (such as in certain lighting, or when you are reading), the pigments in the iris can spread apart, changing the color. Pupil size can also change with certain emotions.

    Eye Color Rarities

    • When very little or no pigment is present, a person is said to be an Albino. Albinos have red or pink irises. Albinos' eyes are quite vulnerable to the sun's UV radiation. Heterochromia is the condition in which a person has eyes of two different colors. It is rare but not considered a medical concern.

    Want to Change Your Eye Color?

    • Prescription colored contact lenses allow you to pick your own eye color and change it day to day if you want. The safest route is to get a doctor's prescription instead of buying them over the Internet.

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