They say that the “eyes are the windows to the soul”. And a pair of eyes that are differently colored or multi-colored (as with the case of heterochromia) definitely create a sense of enigma and mystery, and pique our interest without a doubt, especially in Asian countries.
Celebrities and renowned personalities like Mila Kunis, Kate Bosworth, Christopher Walken, Alexander the Great have heterochromia.
What is heterochromia?
Heterochromia traces its origins to the Greek language, with ‘heteros’ meaning different and ‘chroma’ implying color. This condition is also known as heterochromia iridis and heterochromia iridium.
The melanocytes of the iris consists of pseudosyncytium. This controls the color of the eyes. There are two genes that specialize in the maintenance of the eye color, namely:
- EYCL3, which is found on chromosome 15 that manufactures brown or blue eye color (BEY), and
- EYCL1, which is found on chromosome 19 that imparts green or blue color to the eyes (GEY).
Researchers have found the reason behind blue, green, and brown pigments. However, other unique hues in the constellation of colors are still unknown.
Scientists have also found that there are other genes involved. These decide the placement and pattern of the pigment in pupil and/or iris.
- Heterochromia iridium refers to a pair of eyes having different colors. For instance, brown and blue, or blue and gray.
- Heterochromia iridis means that one pupil of an individual’s eye is multi-colored. For example, the same pupil may be brown and blue, or blue and gray. This is a very rare condition. It usually occurs due to an increase or decrease of pigmentation in the iris.
Types of heterochromia
Heterochromia can be broadly categorized into three classifications, depending on the area where the colors are located in the pupil:
Complete heterochromia: This is caused when the color in the iris of one of the eyes varies completely from the color of the iris of the other eye. For instance, one eye may be green, while the other is brown.
Partial or sectoral heterochromia: As suggested by the name, only a part or sector of an iris is differently colored from the rest of it. This can occur to either or both irises. For example, a certain part of the iris may be blue, while the rest is dark brown.
Central heterochromia: Here, the border around the pupil is a different color than the rest of the iris. Spikes of the central color emanate from the pupil towards the middle of the iris. This results in multiple colors in the same eye. For example, a green ring around the pupil and blue in the iris.
Acquired heterochromia: This usually develops in later years of life due to an injury, certain diseases, and medication.
Causes of heterochromia
Our eyes owe their color to melanin pigment deposits that develop in the iris, located at the center of the eyes. Dark brown eyes are rich in melanin deposits, green and blue eyes indicate a lower deposition of this pigment in the iris.
A lack of distribution and concentration of melanin in the iris causes heterochromia. The location of concentration of melanin in the iris determines the type of heterochromia that will become visible.
A vast majority of cases of heterochromia amongst are benign. They are often not a manifestation of an underlying medical condition.
According to another study, most of the cases are not genetic, even if this is possible.
In some cases, the health condition may signal serious diseases, such as
- Sturge-Weber syndrome
- Bloch-Sulzberger syndrome
- Parry-Romberg syndrome
- Waardenburg syndrome
- Horner’s syndrome
- Hirschsprung disease
- Bourneville disease
- von Recklinghausen disease
- Congenital pigmented nevi
- Trauma around the time of birth or in later phases of life
Causes of acquired heterochromia are as below:
- Eye injury
- Inflammation and/or bleeding of the eye
- Glaucoma
- Iris ectropion syndrome
- Tumors of the iris
- Posner-Schlossman syndrome
- Pigment dispersion syndrome
- Medications like Latisse and latanoprost – Latisse, mostly recommended for thickening eyelashes, may lead to changes in color of the iris. On the other hand, latanoprost, prescribed for treating glaucoma, often causes changes in the eye color by 33 per cent, amongst people taking it for more than 5 years.
Learn more amazing facts about the Human Eye here.
