Definition
In iris heterochromia, the color of one eye is different from the other. In humans it occurs only very rarely. Sometimes heterochromia can be an indication of a disease.
This is especially the case with a new heterochromia. More often, central heterochromia occurs, in which a ring in the middle of the iris differs in color from the rest of the iris. There is also sectorial heterochromia, in which a part of the iris stands out in color.
How does heterochromia occur?
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 differs from the other.
This can be congenital. With the so-called heterochromia simplex this happens without any disease value. It is therefore a freak of nature, similar to a birthmark.
However, an iris heterochromia can also be inherited in the context of the Waardenburg syndrome. Here, heterochromia occurs together with other symptoms such as hearing loss, facial malformations and other pigmentation disorders. In Fuchs heterochromic iridocyclitis, the causes are not yet fully understood, but the inflammation of the iris and the ciliary body is persistent.
This leads to a fading of the affected iris. Since the disease is usually unilateral, heterochromia occurs and the affected eye appears brighter. A unilateral melanosis iridis can also be congenital.
In this case, the iris is very strongly 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 forms 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, and sectorial and central heterochromia. In addition to the classification of heterochromia according to affected areas of the eye, it is also possible to make a classification according to causes. The most important distinction here is between heterochromia simplex, which occurs randomly, is congenital and completely harmless, and heterochromia as a symptom of a disease.
Diseases that cause heterochromia are mostly genetic diseases or unilateral diseases of the middle eye skin, which includes the iris. In genetic diseases that cause 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 heterochromia and heterochromia acquired in the course of life can therefore be a diagnostically important distinction. Acquired heterochromia is almost always a symptom of a disease.
- In central heterochromia only the inner part of the iris has a different color, which is visible as a ring around the pupil. It occurs relatively frequently.
- In sectorial heterochromia, on the other hand, only part of the iris is differently colored. This can be, for example, line or wedge-shaped and often runs from the inside to the outside.
