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All About Heterochromia

Today is "National Different Colored Eyes Day," which is medically known as heterochromia.

On National Different Colored Eyes Day, let's look at why dogs (and people) can have different colored eyes. The condition is known as "heterochromia," "heterochromia iridis," or "heterochromia iridum."

Dogs with heterochromia are not affected by it visually in any way. The coloring is based on a dog's genetic makeup which controls the amount of melanin in a dog's eyes. The amount of melanin in a dog's iris is responsible for the color - dogs with the highest amount of melanin have brown eyes while dogs with the lowest amount have blue eyes. A dog can have full or partial heterochromia - in a partial heterochromia, only a section of the iris is a different color from the other. In central heterochromia, the dog's eye is a different color near the pupil's border compared to the rest of the iris. There may also be some amount of the color along the pupil border that radiates out.

Heterochromia tends to appear more in certain breeds, such as Australian Shepherds, Beagles, Border Collies, Chihuahuas, Dachshunds, Great Danes, Shetland Sheepdogs, Siberian Huskies, Smooth Coat Collies, and Welsh Corgis. Heterochromia also often tends to be genetically linked to the merle coloring in dogs. It also is linked to deafness and blindness in dogs.

This site has some examples of dogs with heterochromia. 

Sources: Shively, J & Phemister, RD (1968) "Fine structure of the iris of dogs manifesting heterochromia iridis" American Journal of Ophthalmology, 66(6) December, pp 1152-1162.; Heterochromia, All About Vision,

Photo credit: Exploring via photopin (license)

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