Every so often a cat looks up at you with two different eyes: one sky blue, the other green, yellow or copper. It looks like a trick of the light. It isn’t. The name for it is heterochromia, and in cats it nearly always comes with a white coat.
In short
| What it is | One blue eye and one green, gold or copper. |
|---|---|
| Which cats | White, or mostly white. |
| Why blue? | The eye has no colour pigment, like the white fur. |
| The catch | About 40% of odd-eyed white cats are deaf, often on the blue side. |
Why one eye is blue
A cat’s white patches are places where the colour cells never arrived while the kitten was growing. No colour cells means white fur and pink skin. If the patch reaches an eye, that eye gets no colour either, and it looks blue. The blue isn’t a pigment at all: it’s light scattering in the eye, the same way the sky looks blue.
When a white patch covers one eye and not the other, you get an odd-eyed cat. That’s why you’ll almost never see one in a black or tabby cat with no white.
The ear on the blue side
The same missing colour cells are also needed in the inner ear. Without them, the ear can stop working in the first weeks of life. So white cats are more often deaf, and the bluer the eyes, the higher the chance. According to the ASPCA’s figures:
- 17 to 20% of white cats with no blue eyes are deaf.
- About 40% of odd-eyed white cats are deaf.
- 65 to 85% of white cats with two blue eyes are deaf.
In odd-eyed cats, deafness is more likely in the ear on the blue-eyed side. Many are deaf in that ear only, and hear fine with the other.
Living with a deaf cat
Deaf cats cope well. They feel vibrations through the floor and watch everything. But a deaf street cat can’t hear a car or a dog coming, so they’re safest neutered, fed in a quiet spot away from the road, and, if possible, adopted. If you approach one, come from the front where it can see you, and stamp gently so it feels you coming. Our guide to approaching a shy cat has more.
Breeds with odd eyes
Some breeds are known for them: the Turkish Van, the Turkish Angora, the Khao Manee from Thailand, whose name means white gem, and, more rarely, the Japanese Bobtail. On the street, look for odd eyes in any cat that’s white or mostly white. More rare looks are in the rarest cat coats.
Met a cat with odd eyes? Snap it close up with Island of Cats. It’s one to remember.
