Millstone Times July 2022

Heterochromia, The Eyes Have It! By Pam Teel PET PAGES

Heterochromia is the term used to describe a difference in a person’s eye color. Heterochromia of the eye is caused by variations in the concentration and distribution of melanin, the pigment that gives color to the skin, hair, and eyes. The word “heterochromia” is derived from ancient Greek where “heteros” means different and “chroma” which means color. The condition is also known as heterochromia iridis or heterochromia iridum. Less than 200,000 people in the United States have heterochromia. Some types of heterochromia are common in dogs, cats, and horses. An ophthal mologist can diagnose heterochromia and investigate why it has occurred. Treatment for heterochromia is about managing the underlying causes. There are three main types of heterochromia, the term used to describe when someone has different-colored eyes: • Complete heterochromia • Central heterochromia • Sectoral heterochromia Central heterochromia has different colors within the same eye. It refers to a combination of colors in one eye, and occurs due to uneven distribution of melanin. Eye color is a result of melanin deposits in the iris, which is the part of the eye responsible for dilating and constricting the pupil to control the amount of light that enters. Blue eyes have small amounts of melanin while brown eyes are rich in melanin. Central heterochromia causes a color separation that almost seems to burst from the pupil at the center of the eye. The dominant color of the iris tends to be low in melanin, so the outer hue will almost always be a shade or blue or green. The inner hue doesn’t form a perfect circle, instead shooting out into tiny, firework-like spikes of color. Gold and hazel colors are commonly seen on this inner ring. Iris color may not stay constant throughout a person’s life. For example, many babies are born with blue eyes that darken within the first 3 years of life. This change occurs as melanin develops. Uneven distribution of mela nin leads to central heterochromia and other types of heterochromia. Most cases of heterochromia are present from birth when the condition is called genetic heterochromia. Most cases of heterochromia in humans are benign and occur without any underlying abnormality. According to the Genetic and Rare Diseases Information Center, most cases of heterochromia of the eye occur sporadically in people with no family history of the condition. However, in some cases it could be hereditary. All types of heterochromia affect the level of melanin pigment in the iris, the colored part of the eye. When there’s less melanin in the iris, it appears as a lighter color. Each form of heterochromia can be remarkably different in appearance. If you’ve heard of heterochromia, complete heterochromia is the type that probably comes to mind. It refers to the complete discoloration of one iris, giving the appearance of two different eye colors. The condition, found in people and animals, is usually caused by a harmless, random genetic mu tation before birth. It can also be caused by illness, injury or medication. Siberian huskies are some of the most common and well-known examples of complete heterochromia. About one in every six huskies has complete heterochromia, often coming in the form of one dark brown eye and one icy blue eye. Also called partial heterochromia, sectoral heterochromia may be the most varied form of the condition. It occurs when there are two different colors in the same iris. You’ll be hard-pressed to find two cases of sectoral heter ochromia that look exactly the same. While one person has an eye that’s half-blue and half-brown, another can have a predominantly green eye with a tiny wedge of hazel that cuts through it. People can even experience partial heterochromia in both eyes, each with its own unique pattern of colors. There are many actors with complete, central and sectoral heterochromia that you may not have ever noticed. Some include: Jane Seymour- right eye green, left eye green and brown, David Bowie- his right eye was blue, left

eye brown, Kate Boswick- right eye blue, left eye combination of brown and blue, Mila Kunis- left eye hazel, right eye green, Henrey Cavill- right eye brown and blue, left eye blue, Kief er Sutherland- one eye blue, one eye green, Christopher Walken- blue eyes but green inner rings, Dan Aykroyd- right eye green, left eye brown, Josh Henderson- right eye blue, left eye brown. Virginia Madsen- one green eye and one brown eye, Emilia Clarke star of Game of Thrones- dark blue irises with a hazel ring around them. Heterochromia is usually harmless when present from birth or early de velopment (congenital heterochro mia), but it can also point to an under

lying condition. Less commonly, heterochromia can occur later in life due to disease, injury or the use of certain medications. In most cases, heter ochromia is benign, though it can signal the presence of such conditions as Horner syndrome or Waardenburg syndrome. This is called acquired heter ochromia. Only about 11 out of every 1,000 Americans have heterochromia, a condi tion that results in two differently colored eyes. This trait is commonly found in animals and is relatively rare in humans and, in many human cases, the condition is hardly noticeable.

32 The Millstone Times

July 2022