Anisocoria in Cats: A Closer Look at Your Cat’s Eyes

Have you ever noticed that your cat has one pupil larger than the other? This condition is called anisocoria, and it can occur in cats for various reasons.

A Cat with Anisocoria

While it may seem alarming at first, understanding anisocoria in cats is essential to ensure your kitty’s well-being. We will explore the causes, symptoms, and potential treatments for anisocoria, providing you with valuable insights to help you take care of your beloved pet.

What is Anisocoria?

Anisocoria is a condition that refers to unequal pupil size in cats. It occurs when one eye’s pupil is larger (Mydriasis) or smaller (Miosis) than the other. This condition can be temporary or persistent and may affect cats of all ages and breeds.


Anisocoria is a term derived from the Greek words “aniso” meaning unequal, and “coria” referring to pupils. In cats, it is characterized by a noticeable difference in the size of the pupils between the left and right eyes. While slight variations in pupil size are normal, a significant difference can be indicative of an underlying health issue.


Anisocoria is relatively common in cats, with several contributing factors. While its exact prevalence is difficult to determine, veterinarians encounter this condition frequently during routine examinations. However, as a responsible cat owner, it is essential to be aware of the symptoms and seek veterinary assistance promptly if anisocoria is observed, in case it is something serious.


Anisocoria can be caused by various factors, ranging from benign to potentially serious conditions. Some possible causes include:

  • Injury or trauma to the eye or surrounding structures: A blow to the head or a foreign object entering the eye can lead to anisocoria.
  • Infections: Certain viral, bacterial, or fungal infections can cause unequal pupil sizes in cats.
  • Glaucoma: Increased pressure within the eye can result in anisocoria.
  • Neurological disorders: Conditions affecting the nervous system, such as brain tumors or nerve damage, may lead to unequal pupil size.

Symptoms and Signs of Anisocoria

Unequal Pupil Size

The most apparent and common symptom of anisocoria is the noticeable difference in pupil size between the two eyes. This condition can affect either eye, though it is often more noticeable when the affected eye has a significantly larger or smaller pupil than the healthy eye. The variation in pupil size might be constant or changeable, depending on the underlying cause.

Difficulty with Visual Abilities

In some cases, cats with anisocoria may experience compromised visual abilities. They may display signs of photosensitivity, squinting, or difficulty focusing. It is important to monitor their behavior closely and seek veterinary assistance if any visual impairments are observed.

Diagnosing Anisocoria

Veterinary Examination

If you notice any signs of anisocoria in your cat, it is crucial to seek veterinary attention promptly. Especially if your cat’s anisocoria occurs suddenly, it should be treated as an urgent matter and you must reach out to your veterinarian without delay. While the condition of having unequal-sized pupils by itself doesn’t lead to permanent vision loss, the underlying cause can potentially cause significant harm to your cat’s eyesight.

The veterinarian will begin with a comprehensive physical examination, focusing on the eyes and the surrounding structures. They will assess the size and reactivity of the pupils, evaluate eye movements, and examine the ocular structures for any abnormalities.

Additional Tests

Depending on the initial examination findings and suspected underlying cause, the veterinarian may recommend additional tests for a more accurate diagnosis. These tests may include blood work to assess overall health, ocular pressure measurement to check for glaucoma, or imaging studies such as X-rays or MRI scans to evaluate the presence of any neurological disorders.

Potential Underlying Conditions

Traumatic Eye Injury

One possible cause of anisocoria in cats is injury or trauma to the eye or the surrounding structures. This can occur due to accidents, fights, or foreign objects entering the eye. Prompt veterinary care is necessary to assess the extent of the damage and provide appropriate treatment.


Certain infections, such as iritis, optic neuritis, feline herpesvirus, toxoplasmosis, or fungal eye infections, can lead to anisocoria in cats. In these cases, treatment involves addressing the underlying infection and providing supportive care to alleviate symptoms.


Glaucoma, characterized by increased pressure within the eye, can cause anisocoria in cats. Prompt diagnosis and treatment are essential to prevent irreversible damage to the optic nerve and preserve vision. Treatment may involve medications, surgery, or both, depending on the severity of the condition.

Neurological Disorders

Anisocoria can also be a symptom of various neurological disorders. Conditions such as brain tumors, stroke, or nerve damage can affect the muscles controlling the size of the pupils. Treatment options for underlying neurological disorders vary based on the specific condition and may involve medication, surgery, or supportive care.

Cat with Uneven Pupils
I had a slight difference in pupil size. My hooman took me to the vet, just in case, and they said I am ok.

Treatment Options

Treating the Underlying Cause

The most effective approach to managing anisocoria in cats is to address the underlying cause. Treatment will depend on the specific condition diagnosed by a veterinarian. In cases of infection, appropriate medications will be prescribed. Injuries or trauma may require surgery or supportive care to facilitate healing. Depending on the severity and type of glaucoma or neurological disorder, the veterinarian may recommend surgical intervention, medication, or a combination of both.

Symptomatic Relief

While treating the underlying cause is crucial, certain measures can provide symptomatic relief for cats with anisocoria. These may include managing pain or discomfort, providing a quiet and dimly lit environment to minimize photosensitivity, and applying prescribed ophthalmic medications, such as eye drops or ointments, as instructed by the veterinarian.

Preventive Measures

Maintaining a Safe Environment

Taking preventive measures can reduce the risk of injuries that may lead to anisocoria. Ensure that your cat’s environment is safe and free from potential hazards. Keep chemicals, small objects, and dangerous plants out of reach, and supervise outdoor activities to prevent accidents.

Regular Veterinary Check-ups

Routine veterinary check-ups are essential to monitor your cat’s overall health and detect any early signs of anisocoria or underlying conditions. Regular ophthalmic examinations can help identify any changes in pupil size or ocular health, ensuring timely intervention if needed.

Veterinarian Examining Cat's Eyes

Living with Anisocoria

Monitoring the Condition

If your cat has been diagnosed with anisocoria, regular monitoring is crucial. Keep a close eye on their behavior, especially changes in visual abilities or any unusual symptoms. Maintain open communication with your veterinarian and report any concerns promptly.

Providing Adequate Support and Care

Cats with anisocoria may require additional support and care. Ensure they have a comfortable, stress-free environment and provide them with any prescribed medications or treatments as directed by the veterinarian. Regularly clean and monitor their eyes for any signs of infection or discomfort.

When to Seek Veterinary Assistance

Immediate Attention

Certain signs or symptoms associated with anisocoria require immediate veterinary attention. These may include severe eye pain, sudden vision loss, discharge from the eye, excessive squinting, or noticeable bulging of the eye. If you observe any of these symptoms, contact your veterinarian immediately.

Routine Check-ups

For cats with stable anisocoria and known underlying conditions, routine check-ups and follow-ups are essential. These visits allow your veterinarian to monitor the progression of the condition, evaluate the effectiveness of the treatment plan, and make any necessary adjustments to ensure your cat’s continued well-being.

Closeup of Cat's Eyes

Final Thoughts

Anisocoria in cats, characterized by unequal pupil size, can be a worrisome condition. While it may be a symptom of underlying health issues, it is crucial to remember that timely veterinary attention and appropriate treatment can improve your cat’s overall prognosis. By staying vigilant, providing proper care, and maintaining regular veterinary check-ups, you can help ensure your feline companion’s ocular health and well-being.

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