Cat Pupils Different Sizes: What Anisocuria Means for Your Cat What Is Anisocuria? Anisocuria is the medical term for having pupils of different sizes. While it can look alarming, the significance depends entirely on the underlying cause. In cats, anisocuria warrants veterinary attention because cats are more prone to serious conditions that cause this symptom. The pupils are controlled by two sets of muscles. Damage or dysfunction to either muscle or the nerves controlling them can cause unequal sizing. Some cats have physiological anisocuria, where the pupils are naturally slightly different sizes. This is benign. Serious Causes of Unequal Pupils Horner’s syndrome is a common cause of anisocuria in cats. It results from damage to the sympathetic nerve pathway. Feline anterior uveitis is inflammation inside the eye that can cause the pupil to constrict on the affected side. Glaucoma causes increased pressure inside the eye that can lead to a dilated pupil and severe pain. It is a sight-threatening emergency. Brain injuries, tumors, or infections can affect the nerves controlling the pupils. Less Serious but Still Important Causes Eye trauma can cause inflammation that leads to unequal pupils. Even seemingly minor eye injuries should be evaluated. Feline iris melanoma, a pigmented tumor of the iris, can cause the affected pupil to dilate or change shape. Previous eye surgery or injury can permanently alter pupil size on one side. Some medications can cause temporary pupil size differences. What Your Vet Will Do Your vet will perform a thorough eye examination using an ophthalmoscope. Neurological testing will help determine if the cause is related to nerve damage versus an eye-specific problem. Blood work may be recommended to rule out systemic conditions like hypertension. Depending on findings, referral to a veterinary ophthalmologist might be recommended. Frequently Asked Questions Q: Is anisocuria always a sign of something serious? A: Not always. However, any NEW change in pupil size should be evaluated by a vet. Q: Can high blood pressure cause different pupil sizes in cats? A: Yes, systemic hypertension can cause eye changes including pupil size differences. Q: How quickly should I see a vet? A: Schedule an appointment within 24 to 48 hours. If accompanied by other symptoms, go immediately. Q: Can anisocuria resolve on its own? A: If caused by a minor injury, it can resolve. However, the underlying cause still needs evaluation. Q: Will my cat go blind from anisocuria? A: It depends on the cause. Some causes may not affect vision at all. Veterinary Disclaimer The information provided in this article is for educational purposes only and should not replace professional veterinary advice. Always consult with a qualified veterinarian for diagnosis and treatment of your pet’s health conditions. If your pet is showing signs of illness, seek veterinary care immediately.