Put simply, heterochromia refers to mismatched eye colors in the same person (or animal). Oftentimes heterochromia is a benign ailment that many may even find aesthetically appealing. While some people may choose to hide heterochromia with sunglasses or colored contact lenses, many consider it to be beautiful.

What causes eye color?

Eye color is hereditary, meaning it is inherited from your parents. While there are generalizations about eye color genetics (lighter colors being recessive to dark, for example), the actual science can get very complicated. Eye color is coded for using multiple interacting genes, which allows for a wide range of color shades in humans and many other mammals. (Heterochromia is actually quite common in animals like cats and dogs.) The amount of melanin present in the eyes determines how dark they become. A lack of overall genetic diversity is thought to be one of the contributing causes to heterochromia, as well as possible environmental factors.

Types of heterochromia

Heterochromia can be sectoral, complete or central in nature.

  • Sectoral heterochromia

A section of one iris does not match the color of the rest of that iris.

  • Complete heterochromia

Each eye is a different color.

  • Central heterochromia

The iris contains three colors; one in the center around the pupil, another in a ring around the inner color, and the outer area of the iris having the “true” eye color.

Causes of heterochromia

Prescription eyeglasses may be very common, but heterochromia is incredibly rare. It affects fewer than one percent of the American population and can have many causes, most of them completely benign. However, heterochromia should always be examined by an eye doctor to rule out rare but potentially dangerous causes:

  • Bloch-Sulzberger syndrome
  • Horner’s syndrome
  • Waardenburg syndrome
  • Hirschsprung disease

Acquired heterochromia

Sometimes heterochromia occurs later in life. When this happens, it is usually the result of injury to the eye due to trauma, infections or overuse of some eye medicines. Diabetes may also cause acquired heterochromia. Both malignant and benign eye tumors have also been known to cause changes in eye color. If one or both irises dramatically change color in someone with no previous history of heterochromia, an eye doctor should be immediately consulted.

Does heterochromia affect vision?

Usually heterochromia has no bearing on vision, and there is no known correlation between use of prescription eyeglasses and heterochromia. However, people with heterochromia should still maintain annual eye exams. Hereditary heterochromia will usually present within the first three years of a child’s life, as a baby’s eyes are not yet fully developed. 

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