Heterochromia is an anatomic condition present in some human beings and animals consisting in eyes irises having different colors.
What does define the iris color?
Eyes color is a characteristic that generally comes from genetic inheritance and whose determination is basically due to the amount and distribution of melanin in the iris.
It is common for newborns to have an iris color that looks like a blueish grey. It isn’t until 6 to 10 months of age when the eye color is defined for good, because, before that moment, cells that generate melanin are yet to mature.
Types of heterochromia
There are several types of heterochromia. Some are rare in human beings, while other types are more frequent.
They can be classified as follows.
ACCORDING TO ITS LOCALIZATION
- Heterochromia iridium or complete heterochromia. It is described as the condition for which one iris has different color to the other iris. It is rare in human beings.
- Heterochromia iridis or partial heterochromia. The person has two different colors within one iris. This last case is much more frequent and may occur in the form of central heterochromia (an iris has a ring of one color and the rest of the iris another), or sectorial heterochromia (heterochromia does not have the form of a ring, but instead it affects only a non-ring-shaped section of the iris, as we can see in the following picture).
ACCORDING TO THE MOMENT OF ONSET
- Congenital heterochromia. It is present from the moment the eye reaches its final coloring.
- Acquired heterochromia. It may appear later in life, due to an injury or to other underlying conditions.
Causes originating such colorings may be very diverse, although in most of the cases, it is a congenital disorder, which means that people affected are born with this condition, which isn’t really relevant, as it does not imply any vision alteration whatsoever. In such cases, the difference of color between the two eyes or within the same eye does not change, and ocular function is normal.
However, heterochromia may have other different causes.
- Idiopathic iris heterochromia. It is already present at birth and does not have any pathological cause. Ocular function is completely normal, as it is not associated with any ocular diseases.
- Pathological and congenital iris heterochromia. It is present from birth and it is due to the existence of an underlying congenital disease, such as neurofibromatosis, Waardenburg syndrome or Claude-Bernard-Horne congenital syndrome.
Heterochromia may also be due to diseases or injuries suffered throughout life. Therefore, if changes in iris coloring are observed, it is important to go to the ophthalmologist in order to examine the case and determine whether there is an underlying condition.
Some factors that may cause acquired heterochromia are:
- Siderosis and hemosiderosis. These are iron depositions on the iris. They cause an alteration in normal coloring and usually occur as a consequence of a trauma or injury.
- Glaucoma and some drugs to treat it. Glaucoma and excessive use of eye drops to treat it may lead to an iris coloring alteration.
- Fuch’s heterochromic iridocyclitis. This eye’s anterior chamber inflammation is one of the most common causes of iris coloring alteration.
- Uveitis or ocular inflammation.
- Melanomas or ocular tumors, consisting in an excessive proliferation of cells responsible for synthesizing melanin, melanocytes.
- Other rare diseases
Incidence and famous cases
Despite the low incidence of heterochromia, there are several famous cases, such as those of actresses Kate Bosworth, Mila Kunis, Alice Eve and Jane Seymour, and those of actors Henry Cavill (Superman) and Benedict Cumberbath (Sherlock). The famous case of David Bowie, whose eyes looked different, was, however, due to a different size in eye pupils (anisocoria), caused by a palsy of the nerve responsible for dilating and contracting the pupil. One of his eye pupils was always dilated, which made the iris of that eye look at a first glance as if it was darker than the other.