One of the Dog’s Eyes Are Dilated – Top 3 Reasons Why

Here are a few common reasons that may explain uneven pupil size in dogs. You may have recently noticed only one of the dog’s eyes is dilated.

1. Head trauma or concussions

Your dog may be feeling the effects of a condition like anisocoria following a head injury. This condition occurs when the pupils of the dog’s eyes are different sizes. Your dog may have fallen off somewhere and landed on one side of the head or the dog may have accidentally run into something head-first.

2. Eye injuries like corneal abrasion

Anisocoria isn’t just caused by head injuries. It could also be a result of eye injuries. Only one of the dog’s eyes could become dilated if it got scratched. Corneal ulcers, for example, could happen if a dog started to rub his eyes against a rough surface (like a carpet). It could also happen between play. Another dog may have accidentally scratched your dog’s eye while they were wrestling with one another.

3. Effects of pink eye

The pupil of a dog’s eye can become dilated due to the effects of inflammation like conjunctivitis (sometimes known as pink eyes). Conjunctivitis would typically affect both eyes but in some cases may only affect one eye (hence why you are only seeing pupil dilation on one side).

Pupil dilation can point to a serious underlying health condition, some of which may be related to a neurological disorder. We recommend calling the vet as soon as possible if you notice your dog having uneven pupil sizes.