Eye Health Central

Two Eyes, Two Colours: A Quick Overview Of Heterochromia

Heterochromia Explained


When it comes to rare eye colours, there are very few that equal heterochromia. Well, technically heterochromia can’t be classified as an eye colour; indeed, the very name “heterochromia” refers to two different eye colours in the same individual. People and animals who are born with heterochromia have two distinct eye colours. This could mean a person either has two different coloured irises or two colours inside one iris.

Let’s explore the fascinating science behind eye colour to better understand how heterochromia happens. In this piece, we’ll also reveal a few famous faces who have heterochromia and explain how you could get the look safely with coloured contact lenses.

How Does Eye Colour Work?

Before we focus on heterochromia, it's important to understand the role of brown pigment known as melanin. Understanding how melanin affects eye colour helps explain how heterochromia comes about.

Most people are familiar with the role melanin plays in making our skin and hair appear darker. Basically, the more melanin you have in your body, the darker your skin or hair will look. Interestingly, this pigment can be found in greater or lesser degrees in everyone’s irises. Technically, this means everyone has brown eyes. It’s the amount of melanin in a person’s eyes that determines how their irises reflect colour to the outside world.

Since melanin does a great job absorbing light, people who have more of this compound in their irises tend to reflect back dark brown eyes. Anyone who has lighter coloured eyes like blue, green, or grey, simply has less melanin in their irises.

A person who has heterochromia will have one eye with significantly more melanin than the other, or one eye that has more melanin in one part of the iris than the other.

How Rare Is Heterochromia?

Recent estimates suggest only about one per cent of the global population has heterochromia. The only colours that match heterochromia in terms of rarity include red and grey.

By far, the most common eye colour is brown. Roughly 80% of the global population has some shade of brown eyes. This colour is especially common with people of African or Asian descent.

After brown eyes, blue eyes are the most common at only about 8% of the global population. Almost everyone who has blue eyes is of European ancestry. Slightly less common than blue eyes are amber, hazel, and green.

How Does A Person Get Heterochromia?

In most cases, people with heterochromia inherit it from their parents. Although geneticists don’t understand the specifics of heterochromia heritability, there appears to be a special mutation all of these patients share.

There are a few cases, however, that suggest patients could develop heterochromia as a reaction to certain medications or as a secondary symptom of some kind of disease. For instance, a few glaucoma eye drops have been known to gradually change eye colour over time. Anyone who notices a sudden change in eye colour should immediately schedule an appointment with an eye doctor.

Different Forms Of Heterochromia

Believe it or not, there are actually three major forms of heterochromia. Although all versions of heterochromia involve two different colours in a person’s eyes, there are a few nuances opticians like to point out.

The most obvious form of heterochromia is known as “complete heterochromia.” Basically, people with this condition have two irises that have different hues.

By contrast, some people have what’s known as partial heterochromia in which there are at least two shades of colours within one iris. Sometimes referred to as sectoral heterochromia, this condition could be found in one or two irises.

Lastly, some people have a condition called central heterochromia. Like partial heterochromia, people with central heterochromia have two different colours in one iris. As you’d expect from its name, however, there’s a different colour around the center of the pupil from the surrounding iris.

Are Heterochromia Eyes Dangerous?

There is no data to suggest people with heterochromia are more at risk from any eye diseases than people with other eye colours. There is, however, a good deal of evidence on the health benefits and drawbacks of different eye colours. Depending on what colours a heterochromia patient’s eyes are, should affect how they think of eye care.

Besides giving off a brown pigment, melanin plays a vital role in blocking out the sun’s harmful UV rays. For this reason, people with lighter eyes are more prone to developing UV-related damage over time. Some doctors also believe electronic blue light might be more harmful to people with lighter eyes, however, the data on this issue is still inconclusive.

Just because people with brown eyes have more UV protection, however, doesn’t mean they should neglect to take care of their eyes. Indeed, a recent study shows that people with brown eyes have a higher incidence of cataracts than those with blue eyes. So, no matter what your eye colour (or colours!) be sure to wear UV-blocking glasses whenever you’re outside.

What Is Anisocoria?

One condition that’s often confused with heterochromia is known as anisocoria. While a person with anisocoria might appear to have two different eye colours, the issue has more to do with the pupils than the irises.

People who suffer from anisocoria have two pupils that are different sizes. Depending on the severity of this condition, it might appear as if the anisocoria patient’s larger eye is darker than the smaller one.

Anisocoria could either be passed down genetically or it could be the result of direct trauma to the eyes. Like most cases of heterochromia, anisocoria is usually no cause for concern.

Current estimates suggest at least 20% of people born in any population have some degree of anisocoria. The most famous example of anisocoria is the late singer-songwriter David Bowie, however, it is often reported that he had heterochromia.

Pop Stars And Pets: Who Has Heterochromia?

If you’re a movie buff, then you’ve probably seen at least one star with heterochromia light up the silver screen. Indeed, one of the most successful actors in the Avengers franchise has a slight case of heterochromia. That’s right, Robert Downy Jr. has heterochromatic eyes!

Here are just a few other names of stars with heterochromatic eyes: Mila Kunis, Benedict Cumberbatch, and Christopher Walken.

There are also a few fascinating historical figures that were reputed to have heterochromia. German poet Johann Wolfgang Goethe, Emperor Anastasius I, and Alexander the Great are just a few of world history’s most notable heterochromia people.

It’s not only humans that can develop heterochromia. There are a few species of dogs and cats that are particularly susceptible to this genetic mutation. Probably the most common dog breed with heterochromia is the Alaskan husky, but Great Danes, collies, and corgis are also particularly susceptible to this genetic mutation. For cats, the Sphinx and the Turkish Angora are famed for their heterochromia traits.

Tips For Using Decorative Contact Lenses

It is possible for anyone to experience the beauty and individuality of heterochromia eyes for themselves. coloured contact lenses can easily change the colour of one or both of your eyes, so whether you want a combination of blue/green, blue/brown or brown/green it's all possible.

It is advisable to have a fitting for coloured contact lenses even if you have perfect vision. A well-fitted pair of contact lenses will be comfortable, plus your optometrist will give you support and advice on how to take care of your contact lenses and help keep your eyes healthy and safe.

It is important to wash and dry your hands before touching your lenses and throw lenses away after their wear time expires. You should also avoid wearing lenses while showering, swimming, and sleeping.

For more contact lens safety tips, consider visiting this webpage put together by the NHS.

Get The Eye Colour You Deserve!

Everyone has a different opinion on heterochromatic eyes. Some believe these eyes look glamorous, but others think they look weird. Whatever your opinion, there are ways you could naturally change your eye colour thanks to coloured contact lenses,  you could even match your eyes with your hair colour. Be sure to discuss the possibility of wearing decorative contacts at your next vision check-up so you can achieve the look you’ve always dreamed of. 

Author: John Dreyer Optometrist Bsc(Hons), MCOPTOM, DipCLP
Created: 27 Apr 2023, Last modified: 20 May 2024