Canine Anisocoria

Cuteness may earn compensation through affiliate links in this story.

Canine anisocoria is a medical situation that entails notable variances in the sizes of pupils. If one of your dog's pupils is a lot bigger than the other one, he possibly has anisocoria. The eye condition can occur not only in dogs, but also in cats and human beings, so take note.

Causes of Anisocoria

Anisocoria generally is an indication of a problem with one of the eyes. A lot of different factors can lead to the presence of anisocoria, including wounds to the cornea, cancer inside the eye, glaucoma, the inflammatory condition uveitis, birth defects and iris atrophy, the latter of which involves a decline in the levels of tissue contained inside of the iris. Iris atrophy is the most frequent trigger of anisocoria. Neurological issues like Horner's syndrome can also bring on the condition.


Symptoms of Anisocoria

Looking over your dog's eyes regularly can help clue you into any possible signs of medical disorders. Typical symptoms of canine anisocoria, apart from variations in pupil size, are shifts in their positioning, changes in eye color, fogginess of the cornea, eye discharge, pawing at the eye, excessive squinting, problems with vision and eye discomfort. If you observe any changes in the appearance of your pet's eyes, set up an appointment with the veterinarian immediately. Whether or not the symptoms are related to anisocoria, they require prompt veterinary attention. Outside of visual cues regarding the eyes, dogs with anisocoria might also just seem a lot more exhausted and reluctant to move around than normal -- a possible sign of painful eyes. They also might exhibit uncharacteristic nervous behavior because of the pain.


Aging Canines and Susceptibility to Anisocoria

Although anisocoria can happen in dogs of all age groups, some of its root causes are more common in elderly dogs -- think iris atrophy, for example. Aging dogs are more vulnerable to the degenerative condition, which is a major cause of anisocoria. Despite that, no overall age biases exist in anisocoria. No gender biases for the condition are noted, either.

Smaller and Bigger Pupils Alike


In cases of anisocoria, the unusually small pupil can be the problematic one. At the other end of the spectrum, the unusually large one can also be the culprit. Only your vet can figure out exactly which one is out of the ordinary.

By Naomi Millburn

Pontiac Veterinary Clinic: Anisocoria
Henderson Mobile Veterinary Services: Anisocoria (Uneven Pupil Size)
VCA Animal Hospitals: Anisocoria in Dogs
Clinical Medicine of the Dog and Cat; Michael Schaer


About the Author
Naomi Millburn has been a freelance writer since 2011. Her areas of writing expertise include arts and crafts, literature, linguistics, traveling, fashion and European and East Asian cultures. She holds a Bachelor of Arts in American literature from Aoyama Gakuin University in Tokyo.

Always check with your veterinarian before changing your pet’s diet, medication, or physical activity routines. This information is not a substitute for a vet’s opinion.