Happy Silly Cat

Understanding Anisocoria: Unequal Pupil Size in Cats

Understanding Anisocoria in Cats

Have you ever noticed that one of your cat’s eyes appears larger or smaller than the other? If so, your cat may be suffering from a condition called anisocoria.

Anisocoria refers to the unequal size of the pupils in one or both eyes. In this article, we will discuss the causes, risks, and management of anisocoria in cats.

Definition of Anisocoria

Anisocoria is a medical term derived from two Greek words: An- meaning not, iso- meaning equal, and kore meaning pupil. Together the words mean “unequal pupil size.” In cats, the pupil is a small, round, dark aperture at the center of the iris that regulates the amount of light entering the eye.

The normal range for a cat’s pupils is between 2-4 mm, and a difference greater than 0.5 mm in size between the two is considered anisocoria.

Function of Pupils in Cats

Pupils play a crucial role in a cat’s vision. They regulate how much light enters the eye by opening or closing in response to light intensity.

When the light is bright, the pupils constrict to reduce the amount of light that enters the eye. Similarly, when the light is dim, the pupils dilate to allow more light to enter the eye, enhancing their ability to see in the dark.

Causes of Anisocoria in Cats

Anisocoria in cats can be a sign of serious underlying health problems. The condition can occur suddenly or gradually over time.

Here are some of the most common causes:

-Diseases inside/outside the eye: Uveitis, glaucoma, and trauma to the eye can cause swollen or damaged tissue, leading to anisocoria.

-Neurologic disease: Cancer, tumors, or brain injuries can lead to neurological issues, affecting the communication between the pupils and the brain, leading to anisocoria.

-Infections: Infections such as feline immunodeficiency virus (FIV) and feline leukemia virus (FeLV) can cause inflammation or damage to the eye, leading to anisocoria.

-Toxic plants: Exposure to certain toxic plants such as lilies, azaleas, and tulips can cause anisocoria.

-Cancer: Cancerous tumors affecting the pupil or eye can lead to anisocoria. Can Anisocoria be Fatal or Painful?

Anisocoria itself is not a deadly condition, but it can be a sign of a more severe underlying condition. These severe illnesses can range from head injuries, brain tumors, or other neurological disorders, which can be fatal if left untreated.

Additionally, some of the causes of anisocoria can be incredibly painful, such as glaucoma, an eye disease that can cause blindness and intense pain.

What to Do If Your Cat Has Anisocoria

If you notice that one or both of your cat’s pupils are unequal in size, it’s essential to seek veterinary care immediately. Make an appointment with your vet as soon as possible.

However, if you notice that the anisocoria is sudden, and accompanied by other symptoms like vomiting, your cat may need emergency medical attention. In such situations, rush your cat to the nearest pet emergency-room.

Physical examination: Your vet will start by conducting a thorough physical examination of your cat, looking for other signs of illness or injury. Bloodwork: Depending on the physical exam, your vet may order blood tests to check for any infections, toxins, or cancer.

Imaging: Imaging tests such as X-rays or CT scans of the head may help diagnose neurological issues. Treatment: The treatment of anisocoria in cats depends on the underlying cause.

Eye drops or medication can be given in cases like infections or inflammation, while in cases like tumors, ophthalmic surgery may be needed.


Anisocoria in cats can be a sign of a serious underlying health condition. While it may seem like a harmless condition, it is always best to consult a veterinarian to determine the cause of anisocoria and prescribe appropriate treatment.

It’s essential to be proactive about your cat’s health and be vigilant when it comes to any changes in their physical appearance or behavior. Early detection and treatment of anisocoria can make a world of difference and improve your cat’s chances of recovery.

Frequently Asked Questions About Anisocoria in Cats

Anisocoria is a condition in which one pupil of a cat’s eye appears larger or smaller than the other. It can be concerning, and pet owners may have many questions about the condition.

In this article, we will discuss some frequently asked questions about anisocoria in cats.

Pain and Anisocoria

Q: Can anisocoria be painful? A: Yes, anisocoria can be painful.

Some of the conditions or illnesses that cause anisocoria, such as glaucoma or corneal ulcers, can be very painful. If you notice that your cat is squinting or rubbing at its eyes, it is essential to seek veterinary care immediately.

Q: What is glaucoma, and how does it affect my cat? A: Glaucoma is a disease that damages the optic nerve in the eye due to increased pressure.

It can lead to permanent blindness if left untreated. Glaucoma is a painful condition, and it can cause anisocoria in cats.

Q: Can trauma cause anisocoria? A: Yes, an injury or trauma to the eye can cause anisocoria in cats.

The pupil may appear larger or smaller if it has been damaged. If you notice any signs of trauma to your cat’s eyes, it is crucial to seek veterinary care immediately.

Spontaneous Recovery of Anisocoria

Q: Can anisocoria in cats resolve on its own? A: In some cases, anisocoria can resolve on its own.

However, whether or not spontaneous recovery is possible depends on the underlying cause of the condition. For instance, if the cause is due to an eye infection, anisocoria can improve on its own with appropriate treatment, while other causes, such as trauma or cancer, may need intervention by a vet.

Q: Are there specific causes of anisocoria that have a higher chance of spontaneous recovery? A: Yes, in certain cases, anisocoria can resolve spontaneously.

For instance, if the underlying cause of anisocoria is related to medication or topical exposure to substances accidentally, anisocoria will likely be temporary and recover on its own. However, a thorough diagnosis by a veterinarian is essential.

Risks of Anisocoria

Q: Is anisocoria a veterinary emergency? A: Anisocoria in and of itself is not an emergency condition, but it may indicate a heightened risk for severe health issues such as head injuries, brain tumors, or other neurological disorders that can be fatal.

If the anisocoria is accompanied by other concerning symptoms such as vomiting, seizures, fainting, or sudden collapse, it is crucial to seek medical attention immediately.

Q: What are some of the risks associated with untreated anisocoria?

A: Anisocoria can be a symptom of some severe underlying health issues, such as tumors, infections, or injury, which can lead to vision loss or even blindness if left untreated. While anisocoria may not be a primary health threat, failing to diagnose and treat underlying conditions involving one or both pupils can have severe and long-lasting consequences for a cat’s health and well-being.

Q: Is there a high risk of anisocoria occurring in certain cat breeds? A: There are no specific types of cat breeds that are at a higher risk of developing anisocoria.

However, some cat breeds are more prone to certain illnesses or traumas that can cause anisocoria. For instance, cats with white fur and blue eyes may have a higher risk of developing Progressive Retinal Atrophy (PRA) condition that can cause several eye-related issues, including anisocoria.


Anisocoria in cats is a condition that can arise due to various underlying health issues, and it is crucial to diagnose and treat those issues. While anisocoria can cause distress among pet owners, recognizing the potential causes and seeking prompt veterinary attention can alleviate fears and reduce the risk of severe health consequences or permanent vision loss.

In case of any uncertainties, it is necessary to discuss the treatment plan with the vet comprehensively and heed their advice to ensure your furry friend’s good health. In conclusion, anisocoria is a condition in which one pupil of a cat’s eye appears larger or smaller than the other, which can be a sign of underlying serious health problems.

Pet owners should seek veterinary care immediately if they notice the condition, particularly if accompanied by other symptoms such as vomiting, nausea, or head injuries. Some forms of anisocoria can lead to permanent vision loss or even death if left untreated.

While spontaneous recovery is possible in some cases, early intervention and proper treatment are key factors in providing the best possible outcome for a cat’s health and well-being. It’s crucial for pet owners to be vigilant and proactive about their cat’s health and be aware of the potential risks.

Popular Posts