The marvel of having 2 different coloured eyes, are found in both animals and humans.

The marvel of having eyes of different colours, are found in both animals and humans.

Heterochromia of the eye, or in this case complete heterochromia, is the term given when one iris is a different color from the other. Heterochromia is a result of the relative excess or lack of melanin (a pigment). It may be inherited, or caused by genetic mosaicism -  where cells within the same person have a different genetic makeup, chimerism, disease, or injury.

Most cases of heterochromia are hereditary, caused by a disease or syndrome, or due to an injury. Sometimes one eye may change color following certain diseases or injuries.

This phenomenon is said to be most often seen in animals, especially cats and dogs like the Siberian Husky.




Animals
Although infrequently seen in humans, complete heterochromia is more frequently observed in other species, where it almost always involves one blue eye. The blue eye occurs within a white spot, where melanin is absent from the skin and hair. These species include the cat, particularly breeds such as Turkish Van, Turkish Angora, Khao Manee and (rarely) Japanese Bobtail. These so-called odd-eyed cats are white, or mostly white, with one normal eye (copper, orange, yellow, green), and one blue eye. Among dogs, complete heterochromia is seen often in the Siberian Husky and few other breeds, usually Australian Shepherd and Catahoula Leopard Dog. Horses with complete heterochromia have one brown and one white, gray, or blue eye - complete heterochromia is more common in horses with pinto coloring. Complete heterochromia occurs also in cattle and even water buffalo.

Cat Briciola with pretty and different colour of eyes
Photo credit

June's multi-colored eyes
by Flickr user kakissel

Let us outside, pleeeaase!
by Flickr user Tiger Girl

Photo credit

Nenya (border collie)
by Flickr user fw42

Scarlet, a Siberian husky
by Flickr user Jeffrey Beall

2 Friends with 2 different coloured eyes
by Flickr user nicoleandcoda

Isabella! the Boston Terrier
by Flickr user elvissa

Bowie with one blue eye one brown
by Flickr user Mark J P

Humans
Speaking of humans, heterochromia is not as frequent in humans as it is in animals, however there are enough among us.  Most notably, some famous ones you might not have known:

Canadian comedian Dan Aykroyd

 American actress, model and singer Kate Bosworth

English actress, Alice Eve

American actress Mila Kunis

68th-greatest Israeli of all time, and Israeli basketball coach, Oded Kattash

Just to name a few.



Did You Know?

• Alexander the Great is said to have had 2 different coloured eyes - one hazel and one green. And according to some stories, he may have purposely sought out a horse with the same unique peepers, too.
• Heterochromia iridis is listed as a "rare disease" by the Office of Rare Diseases (ORD) of the National Institutes of Health (NIH). This means that Heterochromia iridis, or a subtype of Heterochromia iridis, affects less than 200,000 people in the US population.

  

  David Headley

• There are different variations of heterochromia. There's complete heterochromia which we've mentioned here, when each eye is a distinctly different color, say, one blue and one brown. Then there is central heterochromia in which the eyes show various colors, such as a blue iris with a golden-brown ring around the pupil. And sectoral heterochromia where one iris has a splash of color that's different from its overall hue, a trait that actress Kate Bosworth has.
• Pakistani-American, David Headley, (born Daood Sayed Gilani), convicted terrorist in the 2008 Mumbai attacks, also had heterocrhomia.

Introduction photo of gray cat by Flickr user wolfsavard