What is iris heterochromia?
In iris heterochromia, the color of one eye is different from that of the other.
It is extremely rare in humans. Sometimes the heterochromia can be an indication of a disease. This is especially the case with a newly developed heterochromia.
Central heterochromia is more common, in which a ring in the center of the iris is different in color from the rest of the iris.
There is also sectoral heterochromia, in which part of the iris is highlighted in color.
How does heterochromia come about?
The eye color depends on the pigmentation of the iris.
A lot of pigment makes the iris appear brown or dark, whereas weakly pigmented eyes appear light and are often blue.
Heterochromia occurs when the pigmentation of one eye is different from the other. This can be innate.
In so-called heterochromia simplex, this happens without any disease value.
So it is a freak of nature, similar to a birthmark. However, iris heterochromia can also be inherited as part of Waardenburg syndrome. Here, heterochromia occurs along with other symptoms such as hearing loss, facial malformations and other pigment disorders.
In Fuchs heterochromic iridocyclitis, causes that have not yet been fully understood lead to persistent inflammation of the iris and the ciliary body.
This causes the affected iris to pale. Since the disease is usually unilateral, heterochromia occurs and the affected eye appears lighter.
Unilateral melanosis iridis can also occur congenitally. The iris is very heavily pigmented so that it appears almost black.
The affected eye appears darker in this case.
Even if the vegetative supply of an eye is disturbed, it can lead to an apparent heterochromia.
Some infections can damage the pigment epithelium. If this happens unilaterally, heterochromia is the result.
Pathogens can be borrelia or herpes viruses, for example
What types of iris heterochromia are there?
A distinction is made between complete iris heterochromia, in which the eye color of one eye can differ from that of the other, from sectorial and central heterochromia.
- In central heterochromia, only the inner area of the iris has a different color, which is visible as a ring around the pupil. It occurs comparatively often.
- In the case of sectoral heterochromia, however, only part of the iris is colored differently. This can be, for example, line-shaped or wedge-shaped and often runs from the inside to the outside.
In addition to classifying heterochromia according to the affected eye areas, it is also possible to classify it according to causes.
The most important distinction here is between heterochromia simplex, which occurs by chance, is innate and completely harmless, and heterochromia as a symptom of a disease.
Diseases that cause heterochromia are mostly genetic diseases or one-sided diseases of the middle skin of the eye, which also includes the iris.
In the case of genetic diseases that lead to heterochromia, heterochromia is usually also congenital.
However, there are also diseases in which heterochromia only develops in the course of life.
This can be the case, for example, with persistent unilateral inflammation of the iris, ciliary body and choroid.
The distinction between congenital heterchromia and heterchromia acquired in the course of life can therefore be a diagnostically important distinction.
Acquired heterochromia is almost always a symptom of an illness.
The different forms of heterochromia also differ greatly in their frequency.
Complete iris heterochromia is very rare.
Due to the rarity, it is very difficult to find exact details.
However, some sources state that true congenital iris heterochromia with no disease value occurs in only 4 in a million people.
Waardenburg syndrome, which can be a cause of iris heterochromia, occurs in one out of 4500 newborns per year.
With around 785,000 newborns in Germany in 2017, only 174 babies would be statistically affected.
Other causes of iris heterochromia may be even less common.
In contrast, sectoral heterochromia occurs much more frequently.
Central heterchromia is even more common.
It occurs mainly with light eye colors.
Is iris heterochromia inherited?
Iris heterochromia, which is not a symptom of a disease, usually appears to be hereditary.
Eye color is strongly controlled by genes, similar to body size or skin color.
The fact that the iris heterochromia can be inherited is also supported by the fact that it can occur in certain breeds of dogs or cats.
However, iris heterochromia can also occur in the context of various diseases.
Some of these diseases appear later in life and have no clear hereditary cause.
Stars and starlets with an iris heterochromia
Iris heterochromia can also be found in some stars.
David Bowie is often cited as an example. And in fact, one eye of the singer appears significantly darker than the other.
However, this is not a true heterochromia.
David Bowie was involved in a brawl as a teenager in which one of his eyes was damaged. The consequences of this damage were visible to him throughout his life. Well-known actors with iris heterochromia include Kate Bosworth or c. Mila Kunis is said to have iris heterochromia, but it is only visible in certain pictures.
Some historical personalities are also said to have different colored eyes.
Alexander the Great is said to have two differently colored eyes and even rode a horse with this quality. However, these narratives are controversial.
Is that combined with diseases?
Iris heterochromia can, but does not have to, occur as part of a disease.
Iris - heterochromia that are innate and not accompanied by any other symptoms are usually a perfectly harmless freak of nature.
However, iris heterochromia can also occur in some genetic diseases such as Waardenburg syndrome. Here it is often combined with hearing loss and other symptoms.
A newly emerging iris heterochromia is almost always a symptom of a disease. It should therefore be examined by an ophthalmologist.
This is of particular importance if additional symptoms such as pain, imbalance of the pupils or visual disturbances occur.