Cats are devious in many ways, but perhaps their signature trick is looking wonderful to hide their inner cruelty. And the secret ingredient is often their eye colour.
The eye colours that cats can have are broad and various. They may be blue, copper, yellow, orange, green, red, one of each, or some kind of marble pattern. Let’s take a closer look.
Cat eye colours: how do they happen?
As with humans, the coloured part of a cat’s eye is the iris – the next circle out from the pupil. The iris has two layers. Each of these layers contains melanocytes, which produce pigment (colour). This pigment is called melanin.
Anyway, the more melanocytes in a cat’s eye, the darker and more vibrant the colour. This is particularly notable in purebred cats. The parents are carefully selected for clarity of eye colour among other things. And like humans, their kittens inherit the genes of their parents, deferring to the dominant gene.
What about blue-eyed cats?
Blue-eyed cats are not rare, but they are genetically unusual. Some breeds always have blue eyes, while others have them sometimes.
Blue eyes in cats is often a form of albinism. All cats are born with what appear to be blue eyes. In fact, there is not yet any pigment in them, and the blue colour is a trick of the light. But most kittens develop that pigment within a few weeks, and you’ll observe their eyes becoming colourful.
Cats that don’t develop melanin end up keeping their blue eyes for good. So don’t be fooled into believing your blue-eyed beast is a little angel. It’s a genetic thing. Other cats produce the melanin, but due to genetics it is masked or suppressed.
A white cat with very pale blue or even pink eyes is a true albino. The pink in its eyes is from the blood vessels reflecting through from the back, because there’s no melanin to cover them up.
Cats with odd eyes
Sometimes we end up with a moggy whose eyes don’t match. This condition is called heterochromia. Same if a cat has multiple colours within the same eye. It can just see just fine. If he refuses to make eye contact with you, it’s not because it has trouble seeing. It’s because it’s a cat. And also because it’s sick of everyone staring at its odd eyes.
Be warned that if you name your odd-eyed cat after David Bowie, then David Bowie fans will boringly correct you: the thin white duke did not actually have odd-coloured eyes. It’s just that one of them looked darker because one pupil was permanently dilated. For this reason, it is better to name your cat after Dan Aykroyd, a genuine heterochromia.
Being a genetic thing, heterochromia often recurs in the same breeds of cat. If you’re hoping to find one, put your name down for a Turkish Van, Turkish angora, Japanese bobtail, or sphinx. No guarantee, but these brands are more likely to have odd eyes than many other makes of cat.
And it’s more or less the same deal as with blue-eyed cats. In the case of heterochromia cats, something in their genes prevents the melanin from doing its thing in just one of their eyes. If a cat’s eyes are both multi-coloured, it just means that the melanin is unevenly concentrated throughout the irises. A modelling career awaits it.
Other coloured eyes
A cat with green eyes has just a bit more melanin going on than a blue-eyed cat. But the intensity of that green depends on the melanocyte activity. The darkest cat eyes are no darker than rich shade of copper. They may seem darker depending how much light is on them, or how intense they are. But they’re copper.
Cat eye colour and health
Around one in five odd-eyed cats are born deaf. Hearing problems are also common among blue-eyed cats, as the same gene that suppresses the melanin affects cells in the ears.
Once your cat is fully-grown, its eye colour should not change any more. If you notice a change, you should get that cat to the vet. It could be a symptom of something wrong, such as glaucoma, an infection, cancer, or autoimmune issues.