Author: Karen L. McGlothlin, DVM, PhD
Lawndale Veterinary Hospital’s surgery technician, Samantha, has a sweet pitbull named Biggie who occasionally visits us for diagnostics to monitor the amount of protein he has in his urine. When he makes his appearances, there are a couple of things that stand out: 1) Biggie is one of the most handsome pittie boys you’ll ever meet and is usually sporting a bow tie or other fashion accessory and 2) Biggie’s eyes are two different colors! Biggie’s right eye is a clear ice blue while his left eye is a golden honey brown (Figure 1). This condition is called heterochromia (from the Greek, heteros = different; chroma = pigmentation) and can be seen in a wide variety of dog breeds, less commonly in cats and horses, and rarely in humans.
Our technician, Carmen, who is a Great Dane enthusiast, recently saw a Great Dane puppy who was at Lawndale Veterinary Hospital to see Dr. Waterman and suggested a blog on the subject of heterochromia. Carmen is on our social media team and had been considering a Facebook post on the subject and has been collecting photographs of pets with heterochromia for a while (Figure 2) before generously passing the idea on to me for the subject of a blog.
Heterochromia occurs when differing amounts of melanin, a natural skin pigment that determines hair, eye, and skin color, are deposited in the irises of the eyes. The iris of the eye is the colored portion, and it functions to help regulate the amount of light entering the eye. The more melanin deposited in the iris, the darker the eye color appears (and the less light that filters through the iris); while the lack of melanin in the iris causes the eye to appear blue.
Heterochromia can occur in different forms:
1) Complete heterochromia, also known as heterochromia iridis, occurs when there are two completely different colored eyes, like we saw in Biggie.
2) Sectoral heterochromia occurs when only part of the iris is non-pigmented (blue) and another part is pigmented.
3) Central heterochromia occurs when the center of the iris is a different color to the outer portion, seemingly forming concentric circles of different colors.
Although it can occur in any breed, in dogs and cats, heterochromia is often hereditary, passed on along certain genetic lines. Cat breeds that are more common to show heterochromia include: British Shorthairs, Cornish and Devon Rex, Japanese Bobtails, Munchkins, Persians, Scottish Folds, Siamese, Sphynxes, Turkish Angoras and Turkish Vans. Dog breed that are most commonly heterochromic include: Australian Cattle Dogs, Australian Shepherds, Border Collies, Chihuahuas, Dachshunds, Dalmatians, Great Danes, Shetland Sheepdogs, Siberian Huskies, and ShihTzus.
A change in the color of one of the eyes may also develop later in life, in a process called acquired heterochromia. Acquired heterochromia should be investigated by your veterinarian, as this may occur as a result of injury or illness such as glaucoma or even neoplasia (cancer).
In Biggie’s case, both his eyes were blue when he was a puppy and his left eye started changing color when he was about 10-12 weeks of age (Figure 3). If they are going to change, puppies’ eyes normally change color between 9-12 weeks of age and sometimes change as late as 16 weeks of age, so Biggie has hereditary heterochromia. While there is misinformation out there about potential health problems in hereditarily heterochromic dogs, this does not seem to be true for the most part. There does appear to be a link to deafness in Dalmatians with heterochromia, but most dogs with hereditary heterochromia enjoy normal, good health.
REFERENCES AND RECOMMENDED READINGS
Bauhaus, J.M. 2020. Heterochromia in Dogs: Why Your Dog Has Different Colored Eyes.
Brown, J. 2018. Let’s Talk Cats With Different-Colored Eyes, Or Heterochromia In Cats.
Brown, J. 2018. Let’s Talk Dogs With Different-Colored Eyes, Or Heterochromia In Dogs.