Are There More Gray Eyes in the World
The amount of melanin in the specialised cells of the iris is controlled by as many as 16 genes. Melanin is the pigment that makes eyes brown or blue.
This article explains what eye colour is and what causes it. We also look at how many people in the world have each eye colour and how they are split up.
What do eyes look like?
- The coloured part of the eye is called the iris.
- The pupil, the small black hole in the middle of the eye that helps control how much light gets in, is surrounded by the iris.
What causes eyes to be a particular colour?
Scientists used to think that eye colour came from just one gene and that brown eyes were more common than blue eyes.
- They now know that there is more than one thing that makes eyes a certain colour.
- Eye colour can be caused by as many as 16 genes. Most of these genes have something to do with making, moving, or storing melanin.
- Melanin is a brown pigment that is responsible for the colour of a person’s eyes, hair, and skin.
- There are no different pigments in the eyes that aren’t brown. Instead, because they have less melanin, they take in less light. Because of this, they scatter more light, which makes it reflect along the colour spectrum.
- The iris will look blue if it has the least amount of melanin. Those with a little more melanin, for example, will look green or hazel.
How many people in each country have each eye colour?
The eyes of almost everyone in the world are brown.
- People can also have green, grey, amber, or red eyes. Blue is the second most common colour.
- Some people have different-coloured eyes on each side.
brown brown eyes
Estimates say that 70–79% of the people in the world have brown eyes, making them the most common eye colour in the world.
- In fact, the American Academy of Ophthalmology (AAO) says that around 10,000 years ago, everyone on Earth had brown eyes.
- Today, the AAO says that about half of the people who live in the United States have brown eyes, and that number is higher in Africa and Asia.
- People with brown eyes are less likely than those with lighter eyes to get eye cancer, macular degeneration, or diabetic retinopathy.
- Brown-eyed people, on the other hand, are more likely to get cataracts as they age.
Blue is the second-most common eye colour in the world. About 8–10% of people are thought to have blue eyes.
- In the U.S., this number is about 27%, which is higher.
- Scientists think it is possible to find a common ancestor for all people with blue eyes. This ancestor probably had a genetic change that decreased the amount of melanin in the iris.
- Most people who have blue eyes come from Europe.
About 18% of people in the U.S. and 5% of people around the world have eyes that are a mix of green, orange, and gold.
- People from North Africa, the Middle East, Brazil, and Spain are more likely to have hazel eyes than people from other parts of the world.
About 5% of the world’s people have amber eyes, which have a little more melanin than hazel eyes but not as much as brown eyes.
- People with amber eyes most often come from Asia, Spain, South America, or South Africa.
Only about 2% of the people in the world have green eyes, which makes them very rare in general.
- But green eyes are very common in Ireland and Scotland, as well as other parts of the world.
- About 9% of people in the U.S. have green eyes. This is because many people in the U.S. have ancestors from Ireland and Scotland.
About 3% of the people in the world have grey eyes.
- People with grey eyes have little or no melanin in their iris but more collagen in a part of the eye called the stroma.
- Because the light scatters off the collagen, the eyes look grey.
Can eyes change colour?
Many babies are born with blue eyes, but over the first few months, their eyes change colour as more pigment builds up.
- The eyes of a baby may become less blue or even turn brown, but most changes stop by the time the baby is 1 year old.
- Some people wear coloured contact lenses to change the colour of their eyes because they want to look better.
Eye colour can be changed by health problems.
Heterochromia can happen to anyone at any time in their lives. Possible causes include:
- Eye damage or swelling caused by diabetes, iritis, or uveitis
- Fuchs’ heterochromic cyclitis caused him to develop glaucoma. Horner’s syndrome, ocular melanosis, and iris tumour
- Posner-Schlossman syndrome
- The syndrome of Chediak-Higashi
The AAO says that anyone who sees a change in the colour of one or both eyes should see a doctor.
At least 16 genes have something to do with a person’s eye colour.
Most of the pigment melanin is in the iris of brown eyes.
Less melanin makes the eyes lighter. This makes them reflect light less well, which can make them look blue, green, amber, or hazel.
The iris of people with red or violet eyes has little or no melanin.
Around the world, brown eyes are the most common. Scientists think that until about 10,000 years ago, it was the only colour of the eye.
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