5 things you might not know about blue eyes

All about blue eyes

About half as many Americans have blue eyes as brown eyes. Worldwide, around 9% of people have blue eyes. But blue eyes aren’t actually blue. Rather than including a blue pigment, they actually just lack the pigment that makes eyes brown. 

1. Everyone with blue eyes is related

Approximately 11,000 years ago, a baby was born in Europe with a harmless genetic mutation. That little DNA blip was blue eye color.

As far as researchers can tell, this was the first blue-eyed person, and everyone who has blue eyes today is a (very) distant relative of this ancient human.

Before that person, everyone had brown eyes. It was that mutation, which affects the OCA2 gene, that turned off the ability to produce brown eyes in those who have it.

Eye color depends on how much of a pigment called melanin lives in the iris of the eye. Melanin is also responsible for the color of your skin, eyes and hair.

This genetic mutation limits how much melanin is produced in the iris — “diluting” dark brown eyes to a shade of light eyes, like blue.

Because blue eyes have very little melanin, light scatters through the iris in a way that makes them appear blue. This process is known as Tyndall scattering, which is similar to Rayleigh scattering — the phenomena that causes the sky to look blue.

In addition to having significantly less melanin in their irises than people with brown eyes, hazel eyes or green eyes, blue-eyed individuals don’t have very much variation in the part of their DNA responsible for melanin production.

Brown-eyed individuals, on the other hand, have a lot more variation.

This means that everyone with blue eyes can be linked back to one ancestor. Their genetic mutation was inherited at the exact same point.

2. Blue eyes aren't actually blue

Blue eye color is determined by melanin, and melanin is actually brown by nature.

The color of your eyes depends on how much melanin is present in the iris. Brown eyes have the highest amount of melanin in the iris, and blue eyes have the least.

Brown melanin is the only pigment that exists in the eye; there is no pigment for hazel or green — or blue. Eyes only appear to be these colors because of the way light strikes the layers of the iris and reflects back toward the viewer.

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3. You can't predict if a child will have blue eyes

At one time, it was believed that eye color — blue eyes included — was a simple genetic trait. Common knowledge said that you could predict a child’s eye color if you knew the color of their parents’ eyes, and possibly the color of their grandparents’ eyes.

Or so we thought.

Geneticists now know that many different genes influence eye color to some degree — far from the one or two genes that were once believed to determine iris hue.

In addition to genetics, the anatomic structure of the iris can also affect eye color to some degree.

In other words, it’s impossible to know for sure if your children will have blue eyes — or any other color. Both parents may have icy blue eyes, but that’s no guarantee their child’s eyes will be blue at all.

4. Blue eyes at birth doesn't mean blue eyes for life

Human eyes don’t have their full amount of melanin pigment at birth. This is why many babies are born with blue eyes, only to have their eye color change as their irises develop more melanin throughout early childhood.

So don’t be concerned if your child begins to lose their baby-blue eye color. It’s completely normal to see blue become brown, hazel or even green as they get a little older.

This color transition can take anywhere from a few months to three years to run its course.

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5. Blue eyes come with a few risks

Melanin in the iris appears to help protect the back of the eye (the retina) from damage caused by the sun’s UV radiation. Blue eyes contain less melanin than most other eye colors, meaning they may be more at risk of certain damage.

Research has shown that lighter iris colors are associated with:

• A higher risk of ocular uveal melanoma (a type of eye cancer)
• A lower risk of developing cataracts than brown eyes
• A higher risk of developing age-related macular degeneration
• An increased risk of developing alcoholism

Since many people with blue eye color are more sensitive to light and may have a higher risk of retinal damage from UV rays, eye doctors often recommend that people with blue eyes be a little more cautious about their exposure to sunlight.

Eye damage from UV and blue light appears to be related to your lifetime exposure to these rays, so wearing sunglasses that block 100% UV should start during childhood, when possible.

Photochromic lenses are another way to protect blue eyes from UV radiation. These clear lenses block 100% UV radiation both indoors and outside, and automatically darken when they’re exposed to outdoor sunlight.

Keep Your Blue Eyes Healthy

Your eye color may be determined by genetics, but it’s up to you to keep your eyes healthy. Schedule yearly eye exams to monitor your vision and eye health, and contact an eye doctor right away if you notice any dramatic changes in your eyes or vision. 

Regular care and consistent UV protection can go a long way toward keeping your vision clear and your eyes healthy over time.

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