Everything You Need To Know About Heterochromia: Types, Causes & Rarity
The word heterochromia originates from Ancient Greece and means different (heteros) color (chroma). Heterochromia is the condition where the iris (the thin circular structure surrounding the pupil-its role is to control the amount of light reaching the retina) of each eye are differently colored. Heterochromia also exists for the hair and skin. Other terms to describe heterochromia of the iris include heterochromia iridis and heterochromia iridium). There are three types of heterochromia of the iris: complete heterochromia, segmental or sectoral heterochromia, and central heterochromia.
The Three Types Of Heterochromia In Human Eyes
Complete heterochromia is where one iris is completely different in color from the iris of the other eye. Segmental or sectoral heterochromia is where a part of the iris of one or both eyes is distinguished in color from the rest of the iris of that eye. Central heterochromia is distinguished by a different color on the iris at the border of the pupil with spikes of that color radiating outward toward the center of the iris. Celebrities with notable heterochromia include Max Scherzer, Josh Henderson (complete heterochromia); Kate Bosworth, Elizabeth Berkley and Henry Cavill (partial heterochromia); and Paris Hilton, Terrence Howard and Olivia Wilde (central heterochromia). The condition is not restricted to humans, but appears in many other animals as well Venus the Cat has acquired over a million followers on Instagram because of her unique look!
The Causes Of Heterochromia In Human Eyes
The color of the irides develop during the first few months after birth. The levels of the pigment melanin determine how dark the irides will become. The less melanin expressed, the lighter the color of the irides, and vice versa. When the concentration and distribution of melanin are inconsistent, the resulting condition is heterochromia. Most people with heterochromia are born with the condition, which is usually inherited. The condition may also result from a genetic mutation during embryonic development, and sometimes, heterochromia is a symptom of another condition. Horner’s syndrome results when a group of nerves called the sympathetic trunk is damaged and is an example of a condition that causes heterochromia. Waardenburg syndrome is another cause.
Heterochromia That Develops Later In Life
Heterochromia may also develop later in life. The condition is known as acquired heterochromia. There are numerous possible causes of acquired heterochromia including eye injuries, uveitis, some glaucoma medications, and tumors. An example of injury to the eye causing heterochromia may include blunt force trauma to the eye, which leads to bleeding and inflammation, and may also cause permanent loss of vision. Uveitis is the inflammation of the uvea, which is the middle layer of the eye consisting of the iris, choroid and ciliary body, and may be caused by an injury to the eye or inflammatory diseases. Uveitis may also be caused by exposure to toxic chemicals used in the manufacturing process. Tumours formed inside the eye can also cause heterochromia. Tumours can form inside the eye as a symptom of neurofibromatosis, an inherited disorder.
Rarity Of Heterochromia Among Species
Congenital heterochromia is a rare condition affecting about six out of one thousand people. In most cases, the condition is mild and hardly noticeable. Heterochromia of the eyes, skin, and fur, is also rare among animals but it is more common with certain breeds. For dogs, Great Danes, Malamutes, Dalmatians, Border Collies, and Siberian Huskies are sometimes known to experience heterochromia, and among cats, breeds like Khao Manees, Turkish Vans, Japanese Bobtails, and Turkish Angoras more commonly display heterochromia of the irides. Dogs may experience color changes in light blue, dark blue, amber, etc. Cats may experience color changes in orange, yellow, green, copper, etc. Other breeds spotted with this condition include horses, owls, cheetahs, monkeys, hamsters, gerbils, etc.
A Condition Similar To Heterochromia
A condition that on the surface appears similar to heterochromia is called anisocoria, which is the condition of having unequal pupil sizes that make the irides of each eye appear in different colors. The eye with the larger sized pupil tends to appear darker than the other eye although the irides are the same in color. Mild anisocoria is a relatively common condition affecting about twenty percent of the population, but significant anisocoria (one pupil is larger by more than one millimeter) may be the result of eye trauma, certain eye medications, inflammation of the iris, Adie’s syndrome, and some neurological disorders. The late David Bowie was initially thought to have heterochromia, but he had revealed that a fistfight as a teenager left him with anisocoria as one of his pupils remained permanently dilated.