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Heterochromia: 2 different-colored eyes

  1. Causes of heterochromia
  2. Types of Heterochromia
man with heterochromia

Heterochromia is the term used to describe when someone has more than one eye color. In many cases, this means each eye is a different color — for example, one eye is brown and the other eye is green — but it can also mean there are at least two distinct colors in different parts of one eye or both eyes.

Heterochromia is a rare condition that affects the iris, the colored part of the eye. A pigment within the iris called melanin gives eyes their distinct color.

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Heterochromia iridum and heterochromia iridis

When someone’s eyes have any form of multicoloration, they probably have heterochromia iridum or heterochromia iridis. Either name can be used to describe the condition mentioned above: eye-related heterochromia.

Different forms of heterochromia can affect skin and hair, so attaching iridum or iridis clarifies that only the eyes are affected.

Causes of heterochromia

A genetic mutation is believed to cause almost all congenital forms of heterochromia. The mutation is benign, meaning that it doesn’t relate to an underlying disease or illness and won’t cause any harm.

This random genetic “surprise” affects the melanin levels on different parts of the iris(es). Of the common eye colors, brown eyes have the most melanin and blue eyes have the least.

Animals can have heterochromia too. At some point, you’ve probably noticed a dog with two different-colored eyes. Along with other domestic animals, dogs can experience the same genetic phenomenon as humans.

Heterochromia is usually harmless when present from birth or early development (congenital heterochromia), but it can also point to an underlying condition such as Waardenburg syndrome.

Less commonly, heterochromia can occur later in life due to disease, injury or the use of certain medications. This is called acquired heterochromia.

Types of Heterochromia

There are three main types of heterochromia, each with its own unique visual traits:

  • Complete heterochromia: Two “mismatched” eyes of completely different colors.

  • Central heterochromia: Multicolored eyes that start with one color near the pupil, then shift to a different color toward the edge of the iris. It usually affects both eyes.

  • Sectoral heterochromia: Two-colored eyes that take on more of a “slice” or “wedge” pattern on each affected eye. Also called partial heterochromia, it represents the type with the most variety. The secondary color can look like a thin slice of color in one eye and take up two-thirds of the iris in the other. It can occur in one or both eyes.

A condition called anisocoria can easily be confused with heterochromia. It gives the appearance of two different eye colors, but the variation only relates to pupil size — which can cause one eye to look darker than the other — not the actual eye color.

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