This is the Rarest Eye Colour in the World

What determines the shade of your peepers? Experts weigh in on the rarest eye colour in the world—and the genetics behind it.

It’s said that our eyes are the mirrors of our souls, so it makes sense that eye colour is often romanticized. Van Morrison waxed poetic about a brown-eyed girl, while Eric Clapton sang about a woman who “made my blue eyes blue.” Eye colour is a distinct part of your features, unique to you. In fact, no two people in the world have the same colour eyes. And if you’ve ever wondered what the rarest eye colour is, you’re not alone.

While genetics play a role in eye colour, one gene in particular has a large hand in determining the hue.

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What is the rarest eye colour?

It turns out green is the rarest eye colour in the world, with only 2 per cent of the world’s population sporting green peepers.

What is the most common eye colour?

When it comes to the most common eye colour around the world, brown eyes take the cake. The American Academy of Ophthalmology (AAO) reports that as many as 79 per cent of people worldwide have some variation of brown eyes. In fact, it’s an inherited trait that dates back to our early ancestors—about 10,000 years ago, every human on earth had brown eyes, says the AAO.

Not all browns are created equal though. “Eye colour is unique to everyone, and no one brown eye looks like another,” says Purnima Patel, MD, an AAO clinical spokesperson and founder of Ophthalmology and Retina Associates of Georgia.

How common are other eye colours?

Blue eyes are the next most popular eye colour, but they are a more recent evolutionary occurrence, says Dr. Patel. About 27 per cent of Americans have blue eyes, the AAO reports, which is likely due to immigration from Germany, Scandinavia, England, Ireland and Eastern Europe. And here’s the thing: Everyone with blue eyes actually shares one common ancestor. The first-ever pair of baby blues was a genetic fluke that was passed on—and on and on.

The second-rarest eye colour is hazel, a mixture of brown and green with golden flecks. About 5 per cent of the world’s population have hazel eyes. And while violet eyes are a rarity, they’re really just a blue hue, with light bouncing off the surroundings and turning the eyes violet.

What determines eye colour?

In short, eye colour is determined by melanin, which produces hair, eye and skin pigmentation.

The coloured part of your eye, known as the iris, is comprised of two layers: the epithelium in the back, and the stroma in the front. The thin epithelium contains blackish-brown pigments, while the stroma has varying amounts of a pigment called melanin. Eye colour is directly related to the amount of melanin found in the stroma. “People with brown eyes have lots of melanin in the iris, while people with blue eyes have much less,” says Yuna Rapoport, MD, a New York City-based ophthalmologist.

Your iris surrounds your pupil and helps control how much light enters your eye. Light bounces off this melanin in different ways and creates the illusion of various hues, Dr. Patel says. Due to variations in melanin, eye colour runs the gamut from very light blue to very dark brown. Green irises (the rarest eye colour) have less melanin than brown eyes but more than blue eyes, for instance. “Brown is on one end, blue on the other, and hazel and green are in between,” Dr. Patel says. This also means that brown is dominant and blue is the least dominant, also known as recessive.

Melanin also plays a vital function: protecting your eyes. “Melanin prevents the sun’s damaging rays from getting into our eyes and causing cataracts,” Dr. Patel says. “The more melanin you have in your eyes, the lower your risk is.” This means folks with brown eyes may be less likely to develop cataracts or sun-related damage to their eyes than their blue-eyed counterparts.

Learn how to spot the silent signs of eye cataracts.

Do genetics affect eye colour?

Eye colour is quite complex and not as simple as two blue-eyed parents having a blue-eyed child, says Rick Sturm, an associate professor and research fellow at the University of Queensland Frazer Institute in Brisbane, Australia. Sturm’s career is focused on unpacking the genetics of human pigmentation, including eye colour.

“Multiple genes contribute to eye colour, but the main player is OCA2,” he says. In fact, 75 per cent of the genetic contribution to eye colour comes from this gene, which provides instructions for making the P protein found in cells that produce the pigment melanin (melanocytes).

Two genes, OCA2 and HERC2, work together to determine melanin content and, thus, eye colour. “The OCA2 gene sits next to HERC2, and HERC2 has elements that control the regulation of the OCA2 gene,” says Sturm.

Several common variations in the OCA2 gene reduce the amount of P protein, which is why there is a continuum of eye colours from deep brown to grayish blue.

Do other factors determine eye colour?

Yes. Besides genes, the thickness of your iris affects your eye colour. “If it is thinner and you don’t have much melanin, your eyes can look gray,” says Sturm.

Geography matters too, he explains. In Brisbane, Australia, for instance, the breakdown of eye colour is 25 per cent brown, 25 per cent green-hazel and 50 per cent blue. But that differs around the world. “Brown eye colour is predominant in African and Asian populations, and blue eyes are usually predominant in Europe. But the distribution of brown eyes is higher in southern Europe, and blue eyes are more common in northern Europe.”

Sun exposure may also play a role. Sturm has seen freckling in the eyes “that we know is associated with sun exposure.” But the rarest eye colour he’s seen to date is actually polka dots or brown flecks in adolescents. He’s seen it twice, and researchers still don’t know why or how this anomaly occurs, but he doesn’t think it’s due to sun exposure at such a young age.

Can a person have two different coloured eyes?

Yes, a genetic mutation that affects the development of melanin in the irises (called heterochromia) can cause different coloured eyes. In fact, some actors, including Kate Bosworth and Jane Seymour, are known for having the condition. Additionally, if you sustain damage to the nerves of an eye, you can lose eye colour, says Sturm. Plus, glaucoma and certain glaucoma medications have been known to change the colour of your eyes.

Now that you know the rarest eye colour in the world, find out what your hair colour reveals about your health.

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Originally Published on Reader's Digest