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The Science Behind Eye Color

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Eye color is related to genetics and the eye color of our parents and their parents have a strong role to play in whether individuals are born with blue, green, grey or brown eyes or a mix along the color spectrum. Modern science shows new insights that make predicting eye color not quite as transparent as it used to be. Recessive and dominant genes were once thought to play the most significant role in the dominant eye color of offspring. Now there could be 50 genes that have a hand in determining dominant eye color. Learn how eye color is influenced today.

What is the Role of Melanin?

The iris is a circular structure in the eye that helps control how much light reaches the retina. This is typically where color variations are seen in the eye. The amount of the melanin, or pigment, in the eye influences eye color. Those irises with less pigment show up as blue, grey and green eye colors. Brown is the most common eye color and such eyes have the most pigment within the irises. Many Caucasian babies are born with no melanin present at birth, presenting with blue eyes, and change eye color as melanin develops as they age.

Melanin has an important role to play. Melanin protects the structures of the eye from the sun and harmful UV rays. Individuals with blue eyes or less pigment are more sensitive to the dangers of UV rays from electronic devices and the sun than those with brown or black eyes. UV protection is necessary for all but those with light colored eyes or parents of babies with such eye colors should take appropriate measures to protect sensitive eyes from prolonged UV ray exposure.

What about Gene Variation in Dominant Eye Color?

Chromosome 15 is a very special chromosome related to establishing eye color. Two genes, OCA2 and HERC2 lie close together on this chromosome. The P protein produced from the OCA2 gene plays a critical role in the quality and amount of melanin to be present in the iris. Variations is this gene can reduce how much functional P protein is produced and present as less melanin and therefore, lighter eye color. HERC2 has a region called intron 86. A segment of DNA within this region controls the expression of the OCA2 gene. It works like a switch and can turn activity on or off. A polymorphism, or common variation, in the HERC2 gene reduces activity of OCA2, producing lighter-colored eyes.

Other genes that have been found to impact eye color are ASIP, IRF4, TYRP1, TYR, TPCN2, SLC45A2, SLC24A4, and SLC24A5. Some of the aforementioned genes influence skin and hair color. They may also combine to produce a range of eye color in people.

The dominant and recessive eye color inheritance scheme once explained with a simple inheritance pattern is no longer applicable. Though taught to school age children, it can no longer be applied to determining eye color in offspring. Two blue eyed parents can have a child with brown eyes. The multiple genes involved in the eye color inheritance have complicated the original theory.

There are a number of disorders that can influence eye color. A couple include:

  • Ocular albinism: Significantly reduced pigment in the iris causes very light eyes and problems with vision.
  • Oculocutaneous albinism: Individuals present with very light colored irises, white or light-colored hair, and fair skin.

If an unusual variation in eye color has occurred, it is best to get a thorough eye exam to ensure that vision will not be affected by the change in gene expression.

eye color

What about the Stroma?

The stroma is the front layer of the iris. The fibers contained scatter light. Eyes may appear to change color or darken depending on color of clothing worn that ends up temporarily amplifying the scattered light being reflected back.

Is There a Problem when Eyes are Not the Same Color?

A child can present with one blue eye and one brown eye or another combination of eye color. There are a number of reasons and not all are considered serious.

  • Trauma in the womb or right after birth, a benign genetic disorder, and faulty developmental pigment transport can lead to such a condition.
  • In some cases, this difference in eye color can indicate an eye disease, as in Horner’s syndrome.

Early and thorough eye exams can help diagnose any serious condition.

Sealy Eye Center has been serving the eye care needs of the residents of Sealy and the surrounding communities for over 20 years. Call (888) 701-7487 to speak with a friendly Sealy Eye Center associate or contact us online to learn more about eye color and related eye conditions today.