Ever Wondered What Determines The Color of Your Eyes?

Do you like the color of your eyes? Do you wish it was different? Do you wonder what color your children’s eyes will be? Here at Westchester Health, we get these kinds of questions all the time, especially from our younger patients, so we thought we’d create a blog explaining the fascinating subject of eye color.

What makes your eyes the color they are?

Dr Dieck

William B. Dieck, MD, FAAO

There are two main factors that determine your eye color:

1) the amount and pattern of dark brown pigment (called melanin) in the part of your eye called the iris, and

2) the way in which the iris scatters light that passes through the eye. The more important of the two factors is pigment, which is determined by your genes.

It’s all in the genes

Inside the nucleus of your body’s cells are 46 chromosomes, divided into 23 pairs. You inherited one chromosome from each parent to make each pair of your chromosomes.

Chromosomes are made up of strings of DNA called genes. These genes, which also come in pairs, determine the range of characteristics you inherited (hair color, eye color, height, body type, straight or crooked teeth, foot size, and much, much more). Researchers believe that as many as 16 different genes play a role in determining eye color. The two main genes believed to be responsible are OCA2 and HERC2, both of which are part of chromosome 15.

Furthermore, genes are made up of alleles that ultimately determine which particular characteristics you will develop. For most inherited traits, there are generally two alleles. If the two alleles are the same, they are homozygous. If they are different, they are heterozygous.

For each trait, the dominant allele is expressed, while the recessive allele is unexpressed. Recessive alleles are only expressed if there is no dominant allele present.

The alleles for eye color can be separated into blue, green and brown.

  • green alleles are dominant over blue alleles
  • brown alleles are dominant over both blue and green alleles
  • If you received a blue allele and a brown allele, your eye color would be brown because brown is the dominant allele.
  • If you have blue eyes, this means you received blue alleles from both parents.

Your genes also determine your eye color by dictating how much (and where) melanin is produced in your iris. The more melanin produced, the darker the eye color will be.

Why are babies’ eyes blue?

Since melanin production does not begin at birth, babies’ eyes appear blue. Their true eye color will be determined over time. It’s usually not until age three that a child’s permanent eye color becomes apparent.

Can your eye color change?

Have you ever noticed how some people’s eyes seem to change color depending on the lighting? That happens because the iris has two layers and sometimes there is pigment in both layers. In people with blue or green eyes, however, the front layer will have very little or no melanin. Depending on the amount and diffraction of light, their eyes may appear to change colors.

What about people with two different eye colors?

This results from a condition called heterochromia, which occurs due to differences in the early stages of their iris development.

Have questions about your eye color? Come see us.

If you’re concerned about the color of your eyes, or are wondering what eye color you might pass on to your children, please call (914) 232-1919 to make an appointment with one of our Westchester Health eye specialists. He/she will answer all your questions and if needed, perform a thorough eye exam to make sure your eyes are healthy. Whenever, wherever you need us, we’re here for you.

By William B. Dieck, MD, FAAO, Director, Ophthalmology Division, Vice President, Westchester Health, member of Northwell Health Physician Partners

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