Cat eyes come in a variety of beautiful colours. After all, the coloured part of the eye is called the iris, which means rainbow. But have you ever noticed that some cats have two different coloured eyes, known as heterochromia?
Is Heterochromia common in cats?
While heterochromia in humans is relatively rare, heterochromia in cats is far more common. It can result in any number of unusual eye colour combinations, such as one blue eye and one gold eye or one green eye and one blue for instance.
For our feline friends, heterochromia occurs when a white spotting gene, linked to coat colour, blocks the distribution and concentration of pigment in the iris during development. This is why it’s most commonly seen in white cats or cats that have some white in their coat. The gene that causes their fur to be white is the same gene that gives them their unique eye colour.
There are two types of heterochromia:
- Complete heterochromia: A cat has eyes that are two different colours
- Partial or sectoral heterochromia: The iris of one eye has more than one colour
Why is Heterochromia common in cats?
Heterochromia in cats starts when they are kittens. Kittens are born with blue eyes and their true eye colour only begins to show at around 7 to 12 weeks old. During this time, the pigments, known as melanin, in their eyes begin to change. When an adult cat has blue eyes this shows an absence of melanin.
The gene that creates white fur stops the melanin from being able to reach one of the eyes during the kitten’s development. This obstruction causes the melanin to develop and move to just one eye, which leads to two differently coloured irises. In cats who have sectoral heterochromia, the melanin doesn’t spread fully through one eye which leaves it partially blue.
How common are odd-eyed cats?
Odd-eyed cats are surprisingly common. Any kitten could potentially have odd eyes when they are old enough to develop their permanent eye colour. Cat breeds that commonly produce white cats will naturally have a higher occurrence of ‘odd-eyed’ felines compared to others. Breeds where you will most likely see a cat with different coloured eyes, include:
Are cats with different colour eyes rare?
It is very rare for cats with dark or black fur coats to have different coloured eyes. It’s more likely to be found in entirely white cats or those who have some white fur in their coats.
What is the rarest eye colour for cats?
The rarest cat eye colour you will find is the dichromatic or diachronic eye which is generally seen in white cats. This is when there are two colours in one single iris. Cats' eye colours usually vary from blue through yellow to green, orange and brown, while each colour can vary in hue and intensity.
What eye colour is dominant in cats?
The dominant eye colour for adult cats ranges from a greenish-yellow to gold. In most cat breeds, various eye colours were possible. This led to breeds to set a specific eye colour that harmonised with the coat colour and specified it into the standard for that breed.
Are green eyes rare in cats?
Green eyes are often the eye colour most associated with cats and perhaps its no coincidence that it is often linked to luck and mystical powers. However, green eyes are relatively common, especially among mixed-breed moggies.
Are cats with different coloured eyes deaf?
It is a common misconception that cats with different coloured eyes tend to be deaf. Most odd-eyed cats, up to 70% aren't deaf. Meanwhile, around 10 to 20% of cats with the same coloured eyes are born deaf or become deaf later in life as part of the normal feline ageing process. However, white cats who have at least one blue eye have a higher chance of being deaf as the white gene can affect the cochlea soon after birth. If a white kitten has a speck of any other colour on the fur coat, this reduces their chances of being deaf, even if this speck fades as the cat grows.
Heterochromia in cats
While cats with different coloured eyes are relatively common, there is still something mysterious about these special eyed felines that continues to fascinate cat lovers.
