Actor Kate Bosworth is one of many famous faces with the eye condition.
By Annie Hayes
What do actor Kate Bosworth, comedian Dan Aykroyd, and dancer Michael Flatley all have in common? Heterochromia, which describes when a person has two differently-coloured eyes, or eyes that contain more than one colour. More accurately, it refers to the colour of their irises – the pigmented area surrounding the pupil.
There are different types and causes of heterochromia – and it can be very subtle in appearance, or incredibly stark. Sometimes people are born with heterochromia, others get the condition as infants, and some develop it later in life. For some people, it’s a genetic quirk, but it can also occur as a result of injury or disease.
To find out more Nick Wingate, optometrist and director of professional services at the Outside Clinic, and Dr Clare O’Donnell, optometrist and head of research for Optegra, discuss heterochromia causes, varieties and treatment options:
What is heterochromia?
Heterochromia is an umbrella term that refers to a person having different colours in one or both irises. ‘This can manifest as having two different coloured irises, known as complete heterochromia, a different coloured section of a person’s iris, known as segmental heterochromia, or an iris where the central colour is different to the outer ring, known as central heterochromia,’ says Wingate.
Heterochromia is an umbrella term that refers to a person having different colours in one or both irises.
If you have complete heterochromia, one eye could be exclusively blue, and the other could be exclusively brown. If you have segmental heterochromia, an eye could be both colours at the same time – for example, half blue/half brown, or one quarter blue/three quarters brown. And if you have central heterochromia, again, an eye could be both blue and brown, but the colours form staggered rings around the pupil.
If you’re born with different coloured eyes, it’s called congenital heterochromia. Dr O’Donnell explains. When the condition develops later in life due to illness, injury, or medication, it’s known as acquired heterochromia. The condition is also known as heterochromia iridis or heterochromia iridum. Sometime the difference in colour can be very slight, and may only be apparent under certain lighting.
What causes heterochromia?
Heterochromia – and eye colour in general – is caused by variations in the quantity and distribution of melanin in a person’s eyes. Melanin is a pigment that also determines your skin and hair colour. It’s made by cells called melanocytes. While everyone has the same number of these cells, some people make more melanin than others.
‘The general rule is that the less melanin a person has, the lighter their eyes,’ says Wingate. So, blue eyes have small amounts of melanin, while brown eyes have a lot. ‘Eye colour is largely genetic and there may be several genes involved in deciding the colour of your eyes at birth,’ he continues. ‘Our eye colour can also change over time, particularly when we’re younger.’
Heterochromia risk factors
When people are born with heterochromia, they typically have no family history of the condition. Congenital heterochromia doesn’t usually affect a person’s vision or health, although it can be associated with conditions that may, according to Wingate. These include:
- Bloch-Sulzberger syndrome
- Hirschsprung disease
- Waardenburg syndrome
- Von Recklinghausen disease
- Waardenburg syndrome
- Horner’s syndrome
- Bourneville disease
- Parry-Romberg syndrome
- Sturge-Weber syndrome
When heterochromia develops later in life, it can be caused by inflammation, injury, or disease, Wingate continues. The actor Mila Kunis – who has one blue eye and one green eye – famously acquired heterochromia after an eye injury left her blind in one eye as a young child. Some other medical conditions relating to acquired heterochromia include:
- Diabetes
- Glaucoma
- Eye surgery
- Iris tumour
- Iris ectropion syndrome
- Pigment dispersion syndrome
- Posner-Schlossman syndrome
‘The reason the eyes change colour is that the disease process can cause the iris to degenerate and either lose the brown pigment or allow the pigment to shine through the damaged tissue,’ Dr O’Donnell explains. Certain medication associated with glaucoma, such as prostaglandin eye drops, are also associated with the onset of heterochromia.
Heterochromia diagnosis
Heterochromia is easy to identify, since it refers to a colour change within one or both eyes. Unless a medical condition or injury is responsible for the heterochromia, there are usually no other symptoms present. If you develop heterochromia, or you have congenital heterochromia that has changed in appearance, make an appointment with an eye doctor.
If you notice a change in the colour of one or both of your eyes, arrange an eye test to rule out any underlying problems.
‘If you have noticed a change in the colour of one or both of your eyes, you should arrange an eye test with an optometrist to rule out any underlying eye problems like inflammation (uveitis), interruption of nerves connecting the brain and the eye, glaucoma (or the eye drops used to treat it), eye injury, bleeding into the eye or health conditions like diabetes,’ says Dr O’Donnell.
As well as undertake an eye examination, the optometrist may order other tests, such as blood tests and chromosome studies. ‘It’s important to get it checked, because some conditions that cause heterochromia may not cause any symptoms in the early stages, but can lead to sight loss or can even be life threatening over time if they remain untreated.’
Heterochromia treatment
If heterochromia is linked to medical conditions that can affect your vision or lead to health complications, steps will be taken to treat those conditions. ‘The treatment will depend on what the underlying cause is, for example, from anti-inflammatory eye drops when the cause is inflammation, to glaucoma medication if this is the cause,’ says Dr O’Donnell. ‘In very rare cases, anti-cancer treatment may even be indicated if the cause is a tumour damaging the blood supply or nerves to the eye.’
However, if heterochromia is not associated with any other health issues, no treatment is required. Some people choose to wear coloured contact lenses for aesthetic reasons. ‘Treatment of heterochromia is not necessary,’ says Wingate. ‘Some well-known people have it, like [Australian cricketer] Shane Warne and [actor] Benedict Cumberbatch, and it rarely impacts on daily life. However, it can sometimes be a sign of something else, so it’s always worth getting it checked out, just to be on the safe side.’
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