Why Do Some Dogs Have One Blue Eye?

The condition of having only one blue eye is called heterochromia iridis. It is a genetic anomaly caused by a partial or complete lack of pigmentation in the iris of a dog's eye. While it is not necessarily linked to problems in the nervous system or other defects, Dalmatians with one blue eye and one brown eye -- and other animals, such as white cats with only one blue eye and one normal-colored eye -- are often deaf in one or both ears.

  1. Heterochromia Iridis

    • Heterochroma iridis or heterochromia iridum can be caused by eye injury or by a genetic inheritance. Most often, a dog with one blue eye inherited the genetic mutation from both of her parents, which passed the trait on to her. When a dog has one blue eye and one brown eye, it is called complete heterochromia. When a dog has one eye that is partially blue and partially brown or has a blue spot in a brown iris, it is called partial heterochromia or sectoral heterochromia. The blue-colored eye is often called the "affected" eye.

    Eye Color

    • A dog's eye color is is determined by genetics. Eye color is created by a pigment called melanin, which is concentrated in the iris tissue of the eye. The amount of melanin that is present in the iris tissue determines its color. Dogs with a high concentration of melanin will have brown or dark brown eyes. Dogs with a low concentration of melanin will have blue, gray or green eyes.

    About Eyes

    • The eye of a dog consists of three concentric layers or tissues. The outermost layer is the cornea, which is the clear protective outer layer of the eye, and the sclera or the white of the eye. The thick middle layer of the eye is called the uveal tract and consists of the choriod, which contains blood vessels and sits behind the retina, the cilliary body that makes the fluid of the eye that supports the lens, the iris and pupil, which is the opening or black circle located in the center of the iris. The back of the eye contains the retina, which sends visual information to the brain through the optic nerves.

    Common Breeds

    • There are some breeds of dogs that are prone to having only one blue eye due to their genetic makeup. These dogs include Siberian huskies, dalmatians, corgies, border collies, Australian shepherds, Catahoulas, Pyrenees, Great Danes, Pomeranians and dachshunds. Siberian huskies and malamutes often have one solid-colored blue eye and one solid-colored brown eye. Other breeds can have an eye with half or a quarter of its iris blue and the other part brown, and the other eye a solid brown color.