Did you know that having two different-colored eyes is a condition called heterochromia? This is also the term used when one or both of your eyes has more than one color in the iris (the colored part of the eye).
The color of the iris is determined by the amount of a pigment, called melanin, that you have in your body. This pigment helps determine the color of your eyes, hair, and skin. For example, the less melanin you have, the lighter your eyes will be.
Heterochromia most often results from a harmless genetic mutation that happens before birth. This mutation affects the genes that produce melanin, and causes there to be different amounts of melanin in each iris. With different levels of melanin, each eye will be a different color.
Both humans and animals can have heterochromia. It’s much more common among animals, especially domesticated animals such as cats and dogs.
Heterochromia Iridum vs. Heterochromia Iridis
There are different types of heterochromia that can affect a person’s eye, skin, and hair color. The terms “iridium” and “iridis” are both used to refer to heterochromia of the eyes, but each has a specific meaning.
People with heterochromia iridum have two different-colored eyes. For example, they may have one brown eye and one blue eye. In people with heterochromia iridis, the iris in one or both eyes is made up of more than one color.
Causes of Heterochromia
Heterochromia can be present at birth (congenital) and it can also develop it later in life (acquired).
Congenital heterochromia is the type you are born with. Most cases are referred to as benign heterochromia because the condition is harmless and unrelated to any other cause.
When benign heterochromia is ruled out, the most common cause of congenital heterochromia is Horner syndrome. This is a rare condition affecting the eye and tissue around the eye on one side of a person’s face. Heterochromia usually only happens in children who develop Horner syndrome before age 2.
Other causes of congenital heterochromia include:
- Bloch-Sulzberger syndrome
- Bourneville disease
- Hirschsprung disease
- Parry-Romberg syndrome
- Sturge-Weber syndrome
- von Recklinghausen disease
- Waardenburg syndrome
Acquired heterochromia is the type that develops later in life. Possible causes include:
- Eye injury
- Horner syndrome (acquired)
- Benign and malignant tumors of the iris
- Bleeding in the eye
- Eye swelling due to iritis or uveitis
- Eye surgery
- Glaucoma and some medicine used to treat it
- Iris ectropion syndrome
- Ocular melanosis
- Pigment dispersion syndrome
A variety of other conditions can lead to acquired heterochromia, so it’s important to see your eye doctor if you notice any dramatic or unexpected changes to your eye color or vision.
Types of Heterochromia
There are three types of heterochromia:
- Complete heterochromia – This is when one iris in one eye is a completely different color than the iris in the other. For example, you could have one blue eye and one brown eye.
- Central heterochromia – In central heterochromia, a ring of color surrounding the pupil is a different color than the rest of the iris. This inner ring could be brown and the outer ring could be green. Central heterochromia often appears in both eyes.
- Sectoral heterochromia – This condition is also called partial heterochromia and happens when one part of the iris is a different color than the rest. For instance, most of your iris could be brown with a wedge- or slice-shaped area of blue.
If an infant has heterochromia, an eye doctor will typically conduct an eye exam to see if there are any underlying causes. Generally there are no conditions to worry about, but having a baby’s eyes examined can confirm this.
Adults whose eyes have changed color should have an eye exam as soon as possible to determine the cause and get a plan for treatment if needed.
SInce heterochromia is often harmless, no treatment is needed. If your eye doctor finds there is an underlying cause, you would be treated for that specific condition.
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