Have you ever seen someone with two different colour eyes, or look a cat in the (two very different) eyes? They have what is called ‘heterochromia’.
Although it can refer to a patch of hair or skin (or fur) that is a different colour, heterochromia mainly refers to two different coloured eyes. If just part of an iris is different to the remainder of the eye, this is known as partial (or sectoral) heterochromia.
Heterochromia is the result of either an excess or lack of a pigment called melanin. In the case of eyes, the colour of the irises is mainly determined by the concentration and distribution of melanin.
For humans, an excess of melanin in the iris tissues is called hyperplasia, while a lack of melanin is called hypoplasia.
Most cases of heterochromia are hereditary, however, it can also be caused by a disease or injury. This will often result in one eye changing colour, particularly following certain diseases or injuries.
The list of possible causes includes:
In itself, heterochromia is not a health risk and therefore no treatment would be needed. However, if there is a sudden change in the colour of one, or both eyes, it’s important to consult an ophthalmologist. Only an eye examination would reveal whether this might be caused by a medical problem.
A new born or infant with a sign of heterochromia needs to be examined to be certain that there are no related problems. Although there may be no sign of a disorder, it’s valuable to have an examination to be sure. In some instances, blood tests or chromosome tests may be required to confirm the cause.
Interestingly, people with two different colour eyes are often seen as being appealing and film, fashion and the lifestyle media appear to have a particular fascination with famous personalities with heterochromia. Here are a few examples:
Heterochromia also produces some extraordinary looking animals. For many, the appearance of having two different colour eyes is considered exotic and a Google search will provide no end of dramatic examples to be seen.