Heterochromia: Can your eyes be two different colours?
08 October 2021
What is heterochromia?
Heterochromia is the medical term used to describe someone who has more than one eye colour, and it affects less than 1% of the world’s population. The term itself is derived from Ancient Greek, as ‘heteros’ meant different and ‘chroma’ meant colour. In many cases this means that each eye is a different colour – for example, one eye is brown while the other eye is blue. However, it can also mean that there are two separate colours in different parts of the same eye, and this can even occur in both eyes.
Most of the time, heterochromia doesn’t cause any problems to your eye health and it does not affect your vision either. It’s often just another characteristic passed down to your genes through your parents. However, it can also be triggered by a medical condition or trauma to the eye.
The three different types of heterochromia
Did you know that there is more than one type of heterochromia? The three distinct types are complete, central and sectoral:
- Complete heterochromia: Complete heterochromia (heterochromia iridis) is the most common form of heterochromia. This is where one iris is a different colour than the other, e.g. a green eye and a blue eye.
- Central heterochromia: Central heterochromia is where the iris is multi-coloured with one colour that starts near the pupil, shifting to a different colour towards the edge of the iris. This form usually affects both eyes, and it is more subtle than complete heterochromia as the two eyes tend to match each other – rather than being two completely different colours!
- Sectoral heterochromia: Sectoral heterochromia is similar to central heterochromia in that a single iris can have more than one colour, except the colour is more of a ‘slice’ or a ‘wedge’ shape within the iris. Also called partial heterochromia, it’s the form that has the most variety, as it can appear in either one or both eyes and they may not necessarily match each other.
Can animals get heterochromia too?
Believe it or not, heterochromia is actually much more common amongst animals than humans! Only a small percentage of humans have heterochromia, making it quite rare, but it is seen a lot more frequently in animals and it’s a common physical trait. If you’re wondering why that is – put simply, animals are known to breed within their own gene pool. This means that when two animals from the same gene pool (who carry the gene for heterochromia) mate and produce offspring, the offspring is more likely to also have the condition. As inbreeding is more unusual and less common for humans, the gene for heterochromia is typically masked by more dominant genes. However, if two people who both have heterochromia were to produce offspring, it is much more likely that their offspring will also have the condition.
Causes of heterochromia
Heterochromia is a rare condition that affects the iris, which is the coloured part of the eye – which is why it’s a condition that can change your eye colour. The pigment within the iris is called melanin and this is what gives your eyes their distinct colour, based on your genetics.
If you are born with different-coloured eyes, this is called congenital heterochromia. Conditions that could cause this include:
- Benign heterochromia
- Hirschsprung disease
- Bloch-Sulzberger syndrome
- Bourneville disease
- Von Recklinghausen disease
- Sturge-Weber syndrome
- Waardenburg syndrome
- Horner’s syndrome
- Parry-Romberg syndrome
However, if you are not born with the condition and your eye colour changes after infancy, this is called acquired heterochromia. It may be triggered by:
- Eye injuries: Eye injuries are particularly common, with more than 80% of eye injuries happening around the house and during sports and other recreational activities.
- Glaucoma: Glaucoma is an eye disease caused by the build-up of fluid that raises your ocular pressure. It may also lead to vision loss, however early detection and treatment can prevent this.
- Neuroblastoma: Neuroblastoma is a cancer of the nerve cells that typically affects children under 10. When tumours press on the nerves in the body, this can lead to heterochromia. If your child has neuroblastoma and their eye colour changes, please ensure they see their doctor right away.
- Eye cancer: Melanoma can affect the eyes in rare cases. This can happen due to the melanin in our eyes, which is the pigment that gives our eyes their colour. One sign of ocular melanoma is a dark spot on the iris, along with blurry vision or sudden vision loss as other warning signs.
If you have heterochromia and have any worries about the condition affecting your vision, rest assured that it will not have any impact on how well you can see, as it only affects your iris and the colour of your eyes. If you were born with heterochromia there is usually no impact on your eye health as it’s simply a harmless mutation. However, if you have recently acquired it, please visit your doctor to check for any underlying health conditions. Nevertheless, heterochromia will definitely help you to stand out from the crowd with your unique eye colours!
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