This is why some people have 2 different coloured eyes

Tuesday, 11 July 2017 by Callan Smith-Sheerin

Haven’t you heard? Today is different coloured eyes day. You might not realise it, but approximately just under 1% of the world’s population have two eyes of a different colour. As it’s the day to celebrate this fascinating and striking characteristic, we thought we’d explain how it’s caused.


What is heterochromia?

Heterochromia is the name for when someone has a difference of colour in each of their irises. This can be more subtle or it can be quite prominent. Either way, heterochromia is typically harmless and doesn’t affect the quality of your eyesight.

There’s three types of heterochromia that have different effects on the appearance of your iris.

  • Complete heterochromia: One iris is a different colour from the other
  • Sectoral heterochromia: Part of one iris is a different colour from the rest of it
  • Central heterochromia: There's an inner ring around your pupil that's a different colour to the rest of your iris

Kate Bosworth

How do you get heterochromia?

Heterochromia can be either present from birth (congenital) or acquired. Most people will have someone else in their family with the same condition, although if it develops at an early age it’s still considered to be congenital.

Acquired heterochromia can occur either from injury or illness, but won’t be the cause of any difficulty with vision. If any part of your iris does change colour make sure you visit an ophthalmologist, just to be on the safe side.

Why does heterochromia occur?

Your eye colour is set by a variety of genes, but heterochromia occurs due to the concentration and distribution of a pigment called melanin. Melanin is also important in determining what colour skin you have and is found in your hair too.

David Bowie

It’s known that blue eyes contain the lowest amount of melanin, whereas brown eyes have the most, and so heterochromia is caused from one eye having either considerably more or considerably less melanin than the other.

Who has heterochromia?

As we mentioned before, just under 1% of the population have heterochromia. This includes some notable celebrities such as Kate Bosworth, Christopher Walken, Henry Cavill and Mila Kunis. The popularity of these actors has helped to consolidate heterochromia’s reputation as an exotic and glamorous trait.

You may have seen pictures of David Bowie and wonder why we didn’t mention him in that list. The singer, actor and artist is widely believed to have had heterochromia, but instead had a condition called Aniscoria. The pupils in each of his eyes were of different sizes, which made it look as if they were not of the same colour.

Bowie was born with blue eyes, but a scuffle with a schoolfriend over a girl led to him taking a knock that caused his Aniscoria. Don’t worry, the pair must have made up at some point as his opponent, George Underwood, ended up creating the album artwork for Bowie’s Hunky Dory and Rise and Fall of Ziggy Stardust LP’s!

...And finally

Cat heterochromia Heterochromia is not unique to humans. It can be found quite often in particular breeds of dog, such as Siberian huskies, border collies and Shetland sheepdogs, as well as some cats.

That’s enough of a good reason to include a pic of this cute guy!

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