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" means color. The condition is also known as heterochromia iridis or heterochromia iridum.
Contents of this article:
- Less than 200,000 people in the United States have heterochromia. Some types of heterochromia are common in dogs, cats, and horses.
- There are three main types of heterochromia of the eye.
- An ophthalmologist can diagnose heterochromia and investigate why it has occurred.
- Treatment for heterochromia is about managing the underlying causes.
What determines eye color?
Central heterochromia 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.
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 melanin leads to central heterochromia and other types of heterochromia.
Most cases of heterochromia are present from birth when the condition is called genetic heterochromia.
Research suggests that 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, some cases of genetic heterochromia are linked to diseases and syndromes, including:
- Bloch-Sulzberger syndrome
- Bourneville disease
- Hirschsprung disease
- Horner's syndrome
- Parry-Romberg syndrome
- Sturge-Weber syndrome
- von Recklinghausen disease
- Waardenburg syndrome
Heterochromia that develops later in life due to illness, injury, or medication, is known as acquired heterochromia. This is less common than the genetic form.
Diabetes can lead to acquired heterochromia.
Causes of acquired heterochromia include:
- eye surgery
- injury to the eye
- iris ectropion syndrome
- pigment dispersion syndrome
- Posner-Schlossman syndrome
- swelling of the eye
- tumors of the iris
In addition, a medication called latanoprost, which is used to treat glaucoma, has been associated with changes in eye color in up to 33 percent of those taking it for 5 years or longer. Latisse, which is a drug once used to treat glaucoma but now primarily used to thicken eyelashes, may also account for a change in eye color.
Types of eye heterochromia
The different types of heterochromia of the eye include:
Central heterochromia is characterized by having two different colors in the same iris. Usually, the outer ring of the iris is one color while the inner ring is another.
The inner ring often seems to have "spikes" of different colors that radiate from the pupil or the black circle at the center of the iris. Eyes that have this pattern may be referred to as "cat eyes." The outer color is considered to be the true iris color in people with central heterochromia.
Central heterochromia tends to occur in irises that have low levels of melanin.
People with this condition have two different-colored eyes. For example, they may have one blue eye and one brown eye.
In people with sectoral heterochromia, also known as partial heterochromia, one part of the iris is a different color from the rest. Sectoral heterochromia often resembles an irregular spot on the iris of the eye and does not form a ring around the pupil.
Heterochromia of the eye is easy to identify. The person will have two different colored eyes or color differences within one or both eyes.
Color differences may be slight and may only become apparent under certain lighting conditions or in photographs.
Aside from variations in eye color, there are usually no other signs and symptoms of heterochromia. However, if a medical condition or trauma is responsible for the heterochromia, other signs and symptoms may be present.
An optical test can rule out any underlying causes for heterochromia.
Most cases of central heterochromia are benign. They are not linked to medical conditions and do not affect vision or lead to complications. However, a checkup is necessary to rule out other medical conditions.
People who acquire heterochromia and people whose genetic heterochromia changes in appearance should see an eye doctor.
An eye examination will usually be necessary, and other tests, including blood tests and chromosome studies, may be needed.
According to the American Academy of Ophthalmology, if no other issues are present, treatment is not usually necessary. Colored contact lenses may be used for cosmetic reasons if a person with heterochromia wants to alter how their eyes look.
Notable people with central heterochromia
Several celebrities and public figures have forms of heterochromia.
The actors Olivia Wilde, Idina Menzel, and Christopher Walken all have central heterochromia, where the inner ring of the iris is a different color from the outer ring.
Notable people with complete heterochromia, where their two eyes are different colors, include:
- Jane Seymour, actor
- Alice Eve, actor
- Max Scherzer, professional baseball player
- Josh Henderson, actor
- Mila Kunis, an actor who acquired the condition as an adult
Sectoral heterochromia, seen in only part of the iris, affects:
- Kate Bosworth, actor and model
- Henry Cavill, actor
- Elizabeth Berkley, actor