Anisocoria in Cats: Causes, Symptoms, Diagnosis and Treatment

Author: Laura McKinney
Date Of Creation: 4 August 2021
Update Date: 15 December 2024
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The cat's eye is a dynamic structure that allows the animal to be an expert hunter throughout the day. Pupil muscles allow you to control the amount of light that enters the eye and thus improve the quality of images.

When living and playing with your cat, you need to be aware of your pupils as they say a lot about your pet's behavior and health. If you have a cat with a pupil larger than the other then you should continue reading this article by PeritoAnimal to understand what is the anisocoria in cats.

Anisocoria in cats: what is it?

The pupil (black part in the center of the eye) is the orifice located in the central part of the iris (colored part of the eye) and whose function is to regulate the entry of light into the posterior chamber of the eye, acting as a lens of a photographic camera. When the animal is in a bright environment, the pupil does contraction (miosis) and, conversely, when it is in a darker, darker environment, the pupil dilates (mydriasis) so that the animal can see better.


Anisocoria is characterized by the asymmetric or unequal size of pupils, in which one of the pupils is larger (more dilated) or smaller (more contracted) than normal.

Before a cat with a dilated pupil and another one, we should not compare the size of the pupils, note other changes in the appearance of the eye (color change, increased tear production, drooping eyelid) and check if the animal has any discomfort and pain.

Although it appears that this condition is not affecting the animal, if arises suddenly should be considered an emergency case., as it is a sign that something is not right and it is necessary to act quickly.

Anisocoria in cats: causes

It is important to understand that the anisocoria is a symptom and not a disease, but that is reason enough for you to take your pet to the vet. The causes of anisocoria are multiple and varied:


Physiological or congenital

In this case, we have a cat with a pupil larger than the other since birth. It is something that is intrinsic to him and usually poses no risk to his eyesight.

Feline Leukemia Virus (FeLV)

Feline leukemia is a very common virus in cats and can cause lymphoma and affect the nervous system including the nerves that innervate the eye and consequently change the size of the pupils.

Corneal and other eye structures

The cornea is a transparent layer that sits in front of the iris and pupil, which protects them and helps to center light. A corneal injury such as an ulcer can affect the pupil and alter the mechanisms of pupil dilation and contraction. This type of condition is very common due to fights between cats, who use their nails to fight and injure themselves. Injuries from accidents or eye surgery can also result in injuries not only to the cornea, but also to more posterior structures in the eyeball.


synechia

Scar tissue formations within the eye, which result in adhesions between separate structures, altering the architecture of the eye, including the pupils.

iris atrophy

The iris can atrophy, and by atrophying it can change the pupil size of the affected eye. This condition usually arises in older dogs.

unilateral uveitis

The uvea is made up of three ocular structures (iris, ciliary body, and choroidal membrane) and inflammation of one or more structures in the uvea is called uveitis and can affect the size of the pupil, making it generally smaller. Furthermore, uveitis is accompanied by pain.

Glaucoma

Glaucoma is characterized by increased intraocular pressure. This pressure increase results in changes in the structures of the eye and one of the associated symptoms is anisocoria.

Intraocular tumors

Diffuse melanoma of the cat's iris (FDI) is one of the most common tumors and the first symptom is characterized by the presence of hyperpigmented (dark) spots spread throughout the eye that gradually spread or enlarge. As this tumor progresses, the iris architecture is altered and pupil size and pupil abnormalities appear, such as anisocoria or dyschoria (abnormal shape of the pupil). Lymphoma is also one of the most common tumors, and animals often have FeLV.

Injuries to the central nervous system

These injuries can involve traumatic, vascular or tumor situations. Any of these cases can have several consequences on the nervous system, including anisocoria, depending on the location of the lesion and the structures affected.

Horner's Syndrome in Cats

Horner's syndrome in cats is characterized by a set of clinical signs that result from the loss of innervation of the eyeball, due to damage to the facial and ocular nerves that make up the sympathetic nervous system. Normally, only one eye is affected and, in addition to that eye having a more contracted pupil than normal, it has a drooping upper eyelid (eyelid ptosis), enophthalmos (eyeball sinking into the orbit) and protrusion of the third eyelid (the third eyelid is visible when it normally is not).

Certain chemicals or drugs

Certain drops can cause changes in pupil size, as can some flea and organophosphate sprays.

Anisocoria in cats: other symptoms

In all the causes described above we can observe anisocoria and, depending on the adjacent reason, we can observe other symptoms such as:

  • Ache;
  • Eye irritation;
  • Blurry vision;
  • Change in eye color;
  • Change in eye position;
  • Light sensitivity;
  • Eye secretions;
  • drooping eyelids;
  • Blepharospasm (involuntary eyelid twitching);
  • Confusion and disorientation;
  • Apathy.

If the cat does not have any symptoms other than anisocoria, it could be assumed that it is physiological or congenital. On the other hand, if you have any other associated symptoms, it could indicate a specific illness.

Anisocoria in cats: diagnosis

The veterinarian usually doesn't have much difficulty in identifying a cat with a bigger pupil than the other. The real problem is identifying why anisocoria is present. In order to help the veterinarian you must provide all the information about your pet's life and habits.

You will need to undergo a rigorous physical examination, which includes:

  • eye exam: with detailed exploration of ocular structures. Schirmer test (to assess tear production), tonometry (intraocular pressure test - IOP), fluorescein test (to detect corneal ulcers) and examination of the fundus of the eye. During the ophthalmological exam, the place must be dark in order to be able to shine light in each eye of the animal to verify if there is any type of contraction and dilation or if nothing is verified.
  • Complete neurological exam: Test the different reflexes of the nervous system.

During the physical examination, one should look for signs of trauma including ulcers or scratches, and the veterinarian should also find out which pupil is affected to determine whether it is permanently contracted (miosis) or dilated (mydriasis).

Complementary exams may include:

  • Blood count and biochemistry to check the animal's general health;
  • FeLV test;
  • Radiography;
  • Tomography and magnetic resonance, in case of suspicion of neurological origin.

Anisocoria in cats: treatment

Only after the diagnosis is identified can the correct treatment be applied, since the anisocoria does not have direct treatment. It is necessary to find out the reason for this symptom and treat the adjacent disease.

Treatment may include, among other things:

  • Medication or surgery to treat glaucoma;
  • Antibiotics if it is a bacterial infection;
  • Drops to dilate pupils, in case of Horner's syndrome;
  • Withdraw medication that may be affecting the pupils;
  • Surgery for operable tumors, and/or radio or chemotherapy;
  • FeLV is not curable, it can only be supportive treatment to increase the animal's life expectancy.

This article is for information purposes only, at PeritoAnimal.com.br we are not able to prescribe veterinary treatments or perform any type of diagnosis. We suggest that you take your pet to the veterinarian in case it has any type of condition or discomfort.

If you want to read more articles similar to Anisocoria in Cats: Causes, Symptoms, Diagnosis and Treatment, we recommend that you enter our Eye Problems section.