Over the years, I have marveled at the many parent questions I receive that are covered minimally or, in some cases, not at all in medical training nor in the continued learning exercises in which we all participate. I even have a top three. Of these, “how tall is my child going to be?” is actually touched on a little bit, because it’s important to deal with any growth abnormalities. “What should I do about my baby’s ears when we fly?” gets very minimal press. But certainly at the forefront of uncharted (or at least untaught) parent-question territory is: “When will I know what color my baby’s eyes are going to be?”
The appearance of an iris—the differently-colored part of the eye—usually isn’t associated with any disease, which may explain its lack of press. Yet, parents and other interested parties still want to know, which makes the question worth exploring in more detail. In order to do so, let’s get down into the iris and talk about what’s making all those colors.
Eye Pigment Basics
Eye color is determined by the amount of the pigment melanin. This is the same chemical that causes skin pigmentation, and it’s even present in other tissues such as part of the brain. If there’s a lot of melanin in the iris, the eyes are brown; little or no melanin causes the eyes to appear blue. (The blue isn’t due to a special pigment; rather, its appearance is due to the effect of light scattered by particles in the iris. The effect is similar in the atmosphere, which gives us a blue sky. Thus, when the Miners Creek Bluegrass Band sings “Blue Eyes, Blue Skies,” they are definitely onto something.) Hazel and green irises have more melanin than blue and less than brown.
Development of melanin is an ongoing process that requires time and, to some degree, light (think of suntans and freckles). This is why many eventually brown eyes don’t appear that way at birth.
In predicting who will get what color, you may tend to want to go back to your high school biology books, which almost always cover eye color in terms of dominant and recessive genes. Conventional wisdom says that brown is the dominant gene and blue the recessive. Thus, people who have at least one brown-eyed gene will have brown eyes—or so they say! It turns out that the genetics of eye color is more complicated than this, with several genes responsible for eye color. Thus, although not common, blue-eyed parents can have a brown-eyed child. This more complicated inheritance pattern also helps explain those green and hazel eyes. (Read here for a little more regarding the genetics of eye color and a discussion as to why we may not be seeing as many blue eyes in the future.)
That Burning “When” Question
Although most babies will have their eye color determined by 3 to 6 months of age, a substantial number will take longer, often up to a year. Even then, the color is not fixed, and reports abound of color change in childhood or, in some cases, adulthood. The color change may involve either a darkening or lightening and, according to one study published in the Journal of the American Medical Association, may involve 10 to 15 percent of individuals!
Rarely, certain color patterns in the iris can indicate disease. One example is a condition called ocular albinism, which is due to an extremely reduced amount of pigment in the eyes. Patients suffering from this condition have vision problems. Another example is heterochromia, in which each iris is a different color. This can show up in some genetic diseases in addition to a few other conditions. Thus, if your baby’s eyes are two different colors, more evaluation is necessary.
If you have concerns about how your baby’s eyes appear, by all means, bring it up with her provider. For the great majority of babies, however, eye color is an endearing feature that we can cherish in the moment, however it may change in the future. Make those eyes even prettier by gazing at them and talking to them; smiling baby eyes are delightful no matter what the color!