Heterochromia Irides

Heterochromia irides is a disorder of the iris characterized by difference of the iris (plural irises or irides, the most visible part of the eye) in different areas of the same iris. Eye color, specifically the color of the irises, is determined primarily by the concentration and distribution of melanin pigment within the iris tissues. In the heterochromic eye, the iris is characterized by at least two distinct and solidly colored areas or differently colored patches or spots. Heterochromia is uncommon in humans, but quite common in dogs, cats, and horses. Most cases of heterochromia are hereditary, caused by a disease or syndrome, or due to an injury. Sometimes one eye may change color following certain diseases or injuries.

Breeds Affected by Heterochromia Irides

Heterochromia irides is seen in a number of breeds such as Old English Sheepdog, Siberian Husky, American Foxhound, Alaskan Malamute, Shih Tzu. In some cases, it may be accompanied by thinning of the iris, or holes in the iris. Combinations of brown, blue and white are common.

Health Disorders Associated with Heterochromia Irides

In many breeds, a completely blue iris of one eye is acceptable; in other breeds it is rejected for registration. In some breeds, such as Siberian Husky, both irides can be blue. Blue irides in certain breeds, such as Dalmatian, have been associated with deafness and cardiac defects.

Heterochromia irides is also associated with microphthalmia, cataracts, retinal dysplasia, optic nerve hypoplasia (underdeveloped optic nerve) and other eye anomalies. Heterochromia irides is associated with merling gene and coat color in many breeds.

Some breeds in which uveodermatologic syndrome has been reported (for example, Siberian Huskiy, Old English Sheepdog, Australian Shepherd, and Shetland Sheepdog) often have heterochromia irides. Dogs with asymmetric uveal pigmentation may have unilateral ocular changes; therefore, uveodermatologic syndrome should not be excluded as a differential diagnosis on the basis of unilateral clinical signs.

References:
1. UC Davis Book of Dogs : The Complete Medical Reference Guide for Dogs and Puppies Mordecai Siegal
2. Unilateral uveitis in a dog with uveodermatologic syndrome.Sigle KJ, McLellan GJ, Haynes JS, Myers RK, Betts DM.
3. Color Atlas of Veterinary Ophthalmology. Kirk N. Gelat

Canine Eye Diseases and Vision Disorders