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Heterochromia: The Genetics Behind Different Eye Color

Heterochromia is a condition where an individual has different eye color. / Photo by: Tatyana Rychakova via 123rf

 

Many celebrities and famous people captures many audiences because of their beauty and grace. They amaze their fans around the world by their unique facial features that make them outstanding and very different from common people. Aside from an artist’s talents in acting, singing, or dancing, one of the qualities that a person should have to become famous in the showbiz industry is to have a beautiful feature that is not common from anyone in the world. According to an article posted by Fox News, celebrities like Mila Kunis, Jane Seymour, Kate Bosworth, and Wentworth Miller has heterochromia. These celebrities are famous because of their outstanding talent in acting but they also stand out because they embraced their condition.

Moreover, The Tech explained on their website that heterochromia could be an effect of several disorders such as Waardenburg syndrome, Sturge-Weber Syndrome, Horner’s Syndrome, or Parry-Romberg syndrome. Heterochromia could be passed on through genetics and it could be a result of an accident that damaged the eye. Heterochromia rarely happens with humans but they are common with animals. There are a lot of domesticated dogs and cats that are born with different eye color which makes them very attractive to their pet owners.

 

Heterochromia is common with animals like dogs which makes them very attractive to their owners. / Photo by: Mykhailo Polenok via 123rf

 

In a web post by The Odyssey Online, they shared that heterochromia is a genetic mutation. This mutation is resulting in the difference in coloration which happens usually in the iris, but it could also take palace on hair or skin. Heterochromia is determined by the production, delivery, and concentration of melanin which could be inherited or caused by genetic mosaicism, chimerism, disease, or even injury.

The American Academy of Ophthalmology added that heterochromia has many types and causes. An infant can be born with it or develop it soon after birth. In these cases, it is called congenital heterochromia. In most cases, children born with heterochromia will experience no other symptoms. They do not have any other problems with their eyes or general health.

Most people believe that heterochromia is connected with something mystical. There are Native American cultures believe that having heterochromia means that the person can see into heaven and earth at the same time through different colored eyes. They refer to this as having “ghost eyes”. Meanwhile, in Eastern Europe, superstitious people believe that being born with heterochromia means that the person has witch eyes.

Classifications of Heterochromia

Heterochromia iridis is a condition characterized by abnormalities of the iris. Most cases of heterochromia iridis occur sporadically in people with no family history of the condition. However, heterochromia iridis is rarely part of an inherited genetic syndrome. Furthermore, eye color is determined by the concentration and distribution of melanin in the iris. A variety of genetic and acquired factors could have an influence in the final outcome and continued maintenance of the iris color.

Heterochromia is classified primarily by onset: as either genetic or acquired. Although a distinction is frequently made between heterochromia that affects an eye completely or only partially, it is often classified as either genetic or acquired, with mention as to whether the affected iris or portion of the iris is darker or lighter. Most cases of heterochromia are hereditary, caused by certain diseases and syndromes. Sometimes one eye may change color following a disease or injury.

Sectoral or partial heterochromia is sometimes referred to as partial heterochromia where the areas of the same iris contain two completely different colors. It is unknown how rare sectoral heterochromia is in humans. Sectoral heterochromia can sometimes be inherited. When parents pass down different colored eyes to their children, it is often due to something called Waardenburg syndrome. It usually happens in the early stages of development where one cell picks up a mutation in its DNA. maybe some chemical damage or the cell simply made a mistake when it copied its DNA. When there is an abnormal darkening of the iris, it could be a cause of pigment dispersion syndrome. This syndrome is characterized by loss of pigmentation from the posterior iris surface which is disseminated intraocularly and deposited on various intraocular structures, including the anterior surface of the iris.

On the other hand, if the iris is lighter, the person could be exhibiting Waardenburg syndrome. A Japanese research conducted with 11 children with albinism found that they all had sectoral/partial heterochromia.

Acquired heterochromia is usually due to injury, inflammation, the use of certain eye drops that damages the iris, or tumors. Prostaglandin analogs are used topically to lower intraocular pressure in glaucoma patients. A concentric heterochromia has developed in some patients applying these drugs. The stroma around the iris sphincter muscles becomes darker than the peripheral stroma and a stimulation of melanin synthesis within iris melanocytes has been postulated.

Central heterochromia as explained by Science ABC is a condition where the iris has two different colors that surround the pupil like a ring. The outer ring is usually the individual’s actual eye color, while the inner ring radiates out from the pupil. Central heterochromia appears to be prevalent in irises containing low amounts of melanin.

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