One of my puppy's pupils is significantly smaller than the other pupil. Is this normal? What should I do? Pet's info: Dog | Australian Shepherd | Male | unneutered | 2 months and 25 days old

This can be a sign of a head or nerve injury (horners syndrome) and although many resolve slowly over time you should take him to your nearest emergency clinic if any signs of confusion, loss of balance, pain or nausea develop

This could be a neurological problem, an eye problem or a trauma to the head. I strongly recommend having the eyes checked by a vet ASAP.

Anisocoria refers to an unequal pupil size. T his condition causes one of the dog's pupils to be smaller than the other. With the proper detection of the disease's underlying cause, treatment plans are available that should resolve the issue. There are several potential causes of an altered pupil size in dogs, including inflammation in the frontal region of the eye, increased pressure in the eye, diseases that are focused in the iris tissue itself, a poorly developed iris, scar tissue build up in the eye, medications, and cancer (unlikely in a young puppy). I recommend taking Tucker into your vet to have his eye examined. Once the cause is diagnosed, your puppy can get the proper treatment for it.

Have a vet take a look at him to determine if there is a problem. Your vet can do a thorough neurological and eye examination to rule out potential causes. It could be caused by trauma or an infection.

Yes, it is serious when one pupil is smaller than the other. This is known as anisocoria, and it can be caused by an ulcer, disease or injury to the brain, glaucoma, uveitis, retinal disease, and cancer among other causes. When this suddenly appears in a dog's eyes, it's important to have them seen by a vet right away. I would take Sophie into a vet now to have her eyes examined.

It does look like anisocoria, which just means her pupils are two different sizes. A lot of things can cause it, including eye and nervous system problems. I would take Athena to your vet to have her examined to try to figure out what is causing it.

Unequal pupil size (anisocoria) can be caused by traumatic, infection or neurological disorders. It should be addressed by your veterinarian or a veterinary ophthalmologist. Any treatment will depend on the underlying cause. If Leo is lethargic, seems off balance or is bumping into things then he should be seen by a veterinarian today.

My puppy's pupils are different sizes. Is this normal? What to do?

Updated On September 23rd, 2025

Pet's info: Dog | Australian Shepherd | Male | unneutered | 2 months and 25 days old

One of my puppy's pupils is significantly smaller than the other pupil. Is this normal? What should I do?

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Answered By Jennifer Summerfield, DVM CPDT-KA 103

Veterinarian, Certified Dog Trainer

Published on July 5th, 2016

This is a medical condition called [anisocoria](https://www.tuftsyourdog.com/doghealthandmedicine/dog-has-different-sized-pupils/) - most of the time, it indicates either a neurological problem or an injury to one of [the eyes](https://www.petcoach.co/article/sight-development-in-the-dog-puppy). However, occasionally in some puppies this condition may occur intermittently with no obvious cause and no other symptoms associated with it - the cause is as yet unknown, but the puppies are otherwise perfectly normal. If this is the first time you have noticed this, I would recommend taking Tucker to a veterinarian or [veterinary ophthalmologist ](https://www.acvo.org/)for an exam to be on the safe side - he may have an eye or head injury, some type of neurological disease, or been exposed to something toxic that could cause this. If his exam is completely normal and he shows no other symptoms, then in the future you could choose to simply monitor at home for other problems.

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My puppy's pupils are different sizes. Is this normal? What to do?

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