Why do the eyes turn blue

Blue eyes: everything about origins and genetics

From All About Vision

In humans, blue eyes are less common than brown eyes. This is one of the reasons blue contact lenses are so popular.

Here are a few facts about blue eye color that you may not have heard of:

(1) All blue-eyed people could possibly have a common ancestor

It appears that a genetic mutation led to the development of blue eyes in a single person in Europe 6,000 to 10,000 years ago. This is what researchers at the University of Copenhagen have found.

"Originally we all had brown eyes," says Hans Eiberg, associate professor in the Department of Cellular and Molecular Medicine and lead author of the study. "But a genetic mutation that affected the OCA2 gene in our chromosomes created a 'switch' that literally turned off the ability to produce brown eyes."

Eye color depends on the amount of a single type of pigment called melanin in the iris of the eye. This genetic switch, which is located in the gene next to the OCA2 gene, limits the production of melanin in the iris - and thereby "thins" brown eyes into blue.

Blue-eyed people not only have significantly less melanin in their irises than people with brown, hazel, or green eyes, but also little variation in their genetic coding for melanin production. Brown-eyed individuals, on the other hand, have considerable individual variation in the area of ​​their DNA that controls melanin production.

"From this we can conclude that all blue-eyed people are connected to the same ancestor," says Eiberg. "They all inherited the same switch in exactly the same place in their DNA."

So if blue eyes are the result of a genetic mutation in an individual, how did this trait spread from just one person to 20 to 40 percent of Europeans today?

One theory is that blue eyes were immediately seen as an attractive trait. Therefore, more people looked for partners with blue eyes, fathered children with them and thus increased the genetic mutation.

2. Blue eyes do not have a blue pigment

As mentioned earlier, the blue eye color is determined by melanin. Melanin is a brown pigment that regulates the color of our skin, eyes, and hair.

The color of our eyes depends on how much melanin there is in the iris. There is only brown pigment in the eye - no hazel or green or blue. Brown eyes have the highest melanin content in the iris, blue eyes the least.

3. You cannot predict the color of your child's eyes

It used to be believed that eye color - including blue eyes - was a simple genetic trait. That is why it was believed that knowing the color of a child's eyes, and perhaps also that of their grandparents, could predict the color of their eyes.

But geneticists now know that eye color is, to some extent, influenced by up to 16 different genes, not just one or two genes as was once thought. The anatomical structure of the iris can also influence the color of the eyes.

So it's impossible to know for sure if your kids will have blue eyes. Even if you and your partner both have blue eyes, that doesn't guarantee your child's eyes will be blue too.

A royal example of the unpredictability of eye color: Princess Charlotte, daughter of blue-eyed Prince William and green-eyed Kate Middleton, has blue eyes. However, her brother Prince George has brown eyes.

4. Blue eyes at birth do not mean blue eyes for life

At birth, the human eye does not yet have the full pigment content of an adult. Because of this, many babies have blue eyes. However, your eye color changes in early childhood as the eye develops, because more melanin is produced in the iris.

So don't be concerned if your child begins to lose their “baby blue” eye color and their eyes turn green, hazel or brown as they get older.

5. Risks associated with blue eyes

Melanin in the iris of the eye appears to help protect the fundus from damage from UV radiation and high-energy visible light ("blue light") from sunlight and artificial sources.

Because blue eyes contain less melanin than green, hazel, or brown eyes, they may be more prone to damage from UV and blue light.

As for the links between eye color and disease, research has shown that a darker iris compared to a light one has an increased risk of cataract and a decreased risk of ocular choroidal melanoma (a type of eye cancer). However, the same study could not find a connection between eye color and an increased risk of age-related macular degeneration (AMD).

However, many people with blue eyes are sensitive to light and are at increased risk of damaging their retinas from UV light. This is why most ophthalmologists recommend people with blue eyes to be extra careful in sunlight. And since eye damage from UV and blue light is apparently related to lifelong exposure to these rays, wearing sunglasses that are 100 percent UV light and most blue light protective sunglasses should start early in childhood.

Photochromic lenses are another great way to protect blue eyes from UV radiation. These clear lenses block 100 percent of UV radiation both indoors and outdoors and automatically darken in response to sunlight when you go outside. You do not need to wear separate sunglasses.

An anti-reflective coating on photochromic glasses also gives you the best view and comfort in all light conditions - even when driving at night. At the same time, you can bring out your blue eyes with non-reflective glasses. The anti-reflective coating is recommended for all types of glasses, eliminates annoying reflections and allows people to express the beauty and expressiveness of their eyes. It is suitable for all lenses including single vision, multifocal and progressive lenses.

If you use a computer, smartphone, or other digital device for several hours a day, wearing glasses is also a good idea. It can protect your eyes from high-energy blue light.

It can take many years before we understand how risky it is to be constantly exposed to blue lights from computers and smartphones. However, many ophthalmologists believe it is advisable to exercise caution when it comes to protecting your eyes from these devices. Especially if you have blue eyes.

One final note about blue eyes may be of interest to you: Research suggests that blue eyes can increase your risk of alcohol addiction. In a study of blue-eyed Caucasian Americans, it was found that people with this trait were up to 83 percent more likely than people with dark eyes to become addicted to alcohol.

Page published in September 2020

Page updated in May 2021