Have you ever had a friend with two different coloured eyes? Perhaps you are that friend with different coloured eyes? Maybe your eyes have different colours – half and half - in just one eye? Or both? It’s a condition that affects 11 in every 1,000 people in the United States, and it goes by the name of heterochromia.
Heterochromia is a Greek word, and it stands for “differences”. “Heteros” is Greek for different, and “chromia” is the part that refers to the colour itself. Not just any differences, but differences in things such as hair colour, skin colour, or colour of the eyes. That’s where the name for the condition of having two differently-coloured eyes comes from – heterochromia, the Greek word, and central heterochromia, the condition.
There are actually three different types of heterochromia, central heterochromia being just one, and the most prolific. Sectoral heterochromia and complete heterochromia are two other examples of the condition, and the one that you have will depend on how you got it, in a sense. Were you born with the condition, or did you somehow “acquire” it over the course of your life? Generally the condition is known to be genetic, but there are other cases in which a change of eye-colour can occur - injury, for example.
Heterochromia – Types
When looking at heterochromia, it actually classes as an umbrella term for one of three main kinds:
When the centre of the iris of your eye looks one colour, blue, for example, and the outer iris is a different colour, for example a gold or hazel shade, you have central heterochromia. Some people will know and refer to this condition as “cat’s eyes”, because that’s just what it looks like, but it will be the outer part of the iris that gives away the “true” colour of your eyes.
This type of heterochromia is when you have a “patch” of the iris that appears to be a different colour than the rest. It can look a little like a paint-splat on your eye, but it’s not a “complete ring” around the pupil itself. That’s what differentiates sectoral with central heterochromia.
If you have one green eye and one brown eye, you have what is known as complete heterochromia. Each of your eyes are literally different colours, and it’s quite a rare thing. Brown and blue eyes are very different from each other, one being an abundance of melanin, and the other being a complete lack of it.
Heterochromia can occur as a result of a genetic inheritance, or it could occur because of genetic mosaicism, where two different genotypes take precedent when the fertilized embryo is developing. Chimerism is another reason why you may find that you have this change in eye colour, and then there is, of course, injury and disease.