Have you ever seen a person or a dog with different coloured eyes or a multicoloured eye and wondered why they have it or what causes it? The answer is heterochromia iridum.
Heterochromia is an eye condition which results in having different coloured eyes due to the lack of or excess of melanine pigment.
There are two different kinds of it, one is called complete and the other is called partial or otherwise known as sectoral.
Complete heterochromia results in having two completely different coloured eyes.
This is extremely rare in humans but it is more commonly seen in dogs or cats.
Partial or sectoral heterochromia causes different coloured eyes as well, however rather than both eyes being two completely different colours just a part of an eye will be a different colour than the rest of it.
What causes heterochromia? The cause of heterochromia is due to the lack of or excess amount of melanine pigment.
Melanine is a pigment which gives our skin, hair and eyes colour.
If anything affects this melanine pigment from getting to the iris or how it is distributed their will be a change in colouration.
The human eyes are made up of three true colours.
They are brown, yellow and grey.
It is a mix of these three colours together which will produce your eye colour.
This is why the range of eye colours are so vast.
If there is a lot of melanine being distrubuted in the iris the eyes will be brown, if there is a little they will be green and if there is none or very very little they will be blue.
This is why almost all cases of a dog or a cat having complete heterochromia results in having one blue eye.
The melanine was not distributed to that eye making it blue.
How do you get it? There are two ways to get heterochromia.
One is called congenital and the other is called acquired heterochromia.
Congenital is inherited with autosomal dominant trait meaning a gene on one of the non sex chromosones that is always expressed even if there is only one copy of it present.
A single copy of the mutation is enough to cause different coloured eyes i.
e heterochromia.
This is in contrast to a recessive disorder where two copies of the mutation are needed to cause a disease or condition.
The other way to get different heterochromia is to acquire it through injury, disease, inflammation, use of eye drops or tumors.
David Bowie is a good example of someone that has acquired it, his eye got hit in a fight leaving it dilated giving the appearance of different coloured eyes.
Glaucoma patients that use eye drops to help their condition often develop heterochromia because of the extensive use of their eye drops.
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