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One unusual type of eye colouring that is truly ‘eye-catching’ and unusual is heterochromia. The term derives from the Ancient Greek words, “hetero” which translates to different and “chromia” which translates to colour. This term is used to describe the condition where a person has two different coloured eyes, which naturally occurs in approximately six out of 1,000 people (who are born with the condition). The colour of the iris is determined by the pigment melanin. Heterochromia is the result of either an excess or lack of melanin. This means that sometimes due to an uneven distribution of melanin in the eye, an individual’s eyes can sometimes vary slightly; and at other times the eyes can look completely different. But what causes heterochromia and should people with the condition be concerned?

Causes of Heterochromia

The most common cause of heterochromia is congenital (meaning the result of genetics), which is the result of a benign mutation affecting the way melanin (pigment) develops in the irises. In most cases, children born with heterochromia will experience no other symptoms. In other words, it is not an eye disease and it does not affect visual acuity. A few famous examples of congenital heterochromia include Mila Kunis, Jane Seymour, Simon Pegg, and Anthony Stewart Head. The condition also occurs commonly in animals, especially breeds of dogs such as the Siberian Husky, the Border Collie, the Australian Shepherd and the Chihuahua.

While most cases of heterochromia are hereditary, some people who weren’t born with heterochromia might still develop it later in life, as it can be caused by trauma (due to an injury or surgery) or a disease (such as diabetes, viral infections, eye tumours, neurofibromatosis, Waardenburg syndrome or glaucoma). Although acquired heterochromia can often look as interesting as congenital heterochromia, it often can be a sign that the eye has been damaged or unhealthy. For example, the most famous example of acquired heterochromia is David Bowie, whose left iris remained permanently dilated after an injury. Since the fixed pupil doesn’t respond to changes in light when the other pupil does, this gives the illusion of having different coloured eyes.

Different Types of Heterochromia

There are three types of heterochromia, based on where the different colours are located:

1. Complete heterochromia is when one iris is a different colour than the iris of the other eye.

2. Partial heterochromia (or sectoral heterochromia) is where only a portion or sector of the iris of one eye has a different colour than the rest of the iris of that eye. Partial heterochromia can occur in one eye or both eyes and can appear an irregular spot that is a different colour than the rest of the iris eye colour.

3. Central heterochromia, the most common type of heterochromia, is when there is an inner ring that is a different colour than the outer area of the iris. For instance, someone with blue eyes might have a thin ring of green, hazel or brown around their pupils.

Cause for Concern?

All in all, if you have different colour eyes from birth, then there is no need for treatment. However, if you notice a sudden or gradual change in the colour of one or both of your eyes as an adult, it is important to book an appointment with Auckland Eye. One of our ophthalmologists will likely perform a dilated eye exam to rule out any underlying causes and come up with a treatment plan if necessary. Treatment for heterochromia focuses on treating the underlying causes of the condition. However, if there are no other issues with the eyes, no treatment will be needed.

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