Heterochromia, when one eye is different from the other, in color, they say so. The causes can be different and, if you look closely, also the ways in which this manifested asymmetry can be different. The name seems to be that of a rare phenomenon, in truth it is not that much and it can be seen both in people, both in animals such as horse, cat and dog. It can be present from birth, but also appear later and in this case, it may be a symptom of an eye disease.
Heterochromia: what does it mean
It is the name by which a very particular somatic characteristic is defined that to date we can see on average on one person in 100. One eye has a different color to the other, this means, and is explained by the presence of a different concentration of melanin in the two eyes. Usually in one eye, the pigment is more concentrated, so it appears brown, while the other is lighter.
In most cases the heterochromia is genetic origin and can occur more often in animals than in humans. Maybe we pay less attention to it, but so it happens.
There are various types of heterochromia, for example one speaks somatic mosaicism when the different shades are present in the iris of the same eye. An example that perhaps someone has already noticed is Kate Bosworth, with a half blue, half hazel right eye. This is how it appears from birth and it is not a health problem.
Going back in time, we find another famous person who had eyes with abnormal colors, today called heterochromia. I refer to Alexander the Great, famous for quite other reasons and which today we can also associate with this phenomenon. He had, they say, one hazel eye and one green eye.
If it is not linked to genetic reasons, heterochromia can be a consequence of some drugs, one of the side effects. The ones that can cause this chromatic transformation for example, antiglaucoma eye drops, because they would unequally discolor the iris in the two eyes.
L'heterochromia iris as already mentioned, it can also affect only one iris, but usually the most frequent one creates differences between one eye and the other. This happens if individual cells produce different amounts of pigment, it is a consequence of the fact that humans and all multicellular organisms are originated from a single cell, so the genetic heritage is that, but if a variation in the production of melanin appears that affects a cell, it will originate the cells of the iris of one eye, but not the cells of the other eye. Here are the two heterochromatic irises.
This has not always been known, why eye color was initially thought to depend only on one gene, then it was understood that it is determined by the amount of melanin present in the iris, which pigments it. As a rule, the eyes are blue if the amount of pigment is little or no, in the opposite case, they are brown.
In truth, when you find yourself with one eye different from the other in terms of color, following a trauma, we don't talk about heterochromia. In fact the known David Bowie, the recently deceased English singer-songwriter, seemed to have different colored eyes but it is not a case of heterochromia. He had both of them blue but the left turned almost black following a punch in the face.
In this case, the trauma resulted in a paralysis of the constricting nerve of the pupil from the aesthetic point of view it gives the effect of a dilated pupil. Here it is therefore, rather than heterochromia, anisocoria, ie the different size of the two pupils.
Maybe for their big eyes, cats are animals in which the heterochromia is more visible. In truth it has a very similar incidence also in dogs and horses.
When it is a feature that appears from birth, this is it linked to the presence of melanin which also affects skin coloring. This is also evident when one thinks that children with light eyes often have fair skin and so those with darker complexions have dark eyes.
To notice this phenomenon in children, Sometimes it is necessary to wait up to about three years because first they can show only light colored eyes because the production of melanin is not sufficient to be able to provide the final color.
When is the symptom of an eye disease is certainly less "folkloristic" and more worrying! In many cases we can speak of Fuchs heterochromia, an inflammation that usually affects only one eye and creates a loss of iris pigment. Even the pigmentary glaucoma it can be a cause of heterochromia such as nevus of Ota which is a very rare form of unilateral ocular melanoma.
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