Why Do Cats Eyes Dilate? Should You Be Worried?

A British Shorthair Cat with Dilated eyes

Cats have some of the most beautiful eyes in the animal kingdom! Most cat owners will know that slow blinking is a cats way of saying they love you. But you may have noticed your cat’s eyes dilate from time to time. This article explores the different reasons why cats eyes dilate and if you should be worried.

Why Do Cats Eyes Dilate?

A cat’s eyes dilate primarily to improve its vision in low light. . Another reason cats eyes dilate is a reflex to show their mood, temperament, and health. If a cat’s eyes are constantly dilated, indicate severe health issues, including feline leukaemia, toxicity, dysautonomia, and tumours.

Animals’ eyes, including cats’, work similarly to yours. Many of the same eye conditions humans have, such as cataracts, glaucoma, and other diseases, can also affect animals. Your cat must receive proper eye care to protect its vision and enable it to communicate comfortably with its surroundings.

The eye is a complex organ that continually changes the amount of light it lets in and focuses on nearby and distant objects. As a result, it generates a continuous stream of easily transmitted images to the brain.

What Are The Major Causes Of Cats Eyes Dilating? 

The Cats Age And Activity Levels:

If your cat is naturally hyper, her pupils will likely be dilated regularly. Also, younger cats are more likely than older, more relaxed cats to have dilated pupils due to excitement.

Health Problems:

If a cat’s eyes are constantly dilated, this could indicate a severe health condition. If you notice your cat’s eyes are dilated continuously, you should seek the help of a veterinarian as soon as possible.

Improving Eyesight:

The eyes of a cat are incredible. Cats dilate their eyes to allow more light to enter the eye by expanding their pupils, making it easier for cats to see in the dark. They enable a cat to see in near-darkness and give them a strong sense of motion, allowing them to hunt prey. The vertical, slit-shaped cat eyes, on the other hand, fascinate a lot of people. 


Cats communicate through their eyes. The direction of your cat’s gaze will lead you to the topic of her interest. 

In a comfortable, purring cat, a fixed gaze and rigid body posture may indicate aggression, but the same look may be requesting petting or some other kind of affection.

The location of the eyelids and the dilation of the eyes also decide what cats mean. The messages range from subtle to overt, and they can be highly effective. 


Any solid emotional arousal—fear, rage, pleasure, or excitement—can cause the cat’s pupil to contract into a slit suddenly. For example, the cat’s pupil contract can be visible when faced with an entire bowl of a favourite food or a catnip mouse. A cats eyes can even do this when she is startled by the arrival of a new cat.


When cats are alert, they open their eyes wide. Putting one’s eyes wide open to the risk of injury can be a sign of great trust. 


Cat eyes that look unblinkingly from afar may indicate superiority, power, or even violence. This subtle action, which can monitor access to multicat households’ keys, is often overlooked by owners. A single cat can deter and prevent other felines from entering an “owned” pathway to food bowls, litter boxes, or another significant territory simply using this unblinking gaze.


A slit-eyed expression denotes intense emotion, such as fear or aggression. Squinting often protects the eyes from an opponent’s claws. If you lock eyes with a cat you don’t know, you risk being attacked.

Cat Kisses

The eyelids of a happy and trusting kitty are droopy and sleepy-looking. So give your cat a “kitty kiss” by meeting their sleepy eyes with your relaxed gaze and slowly “blinking.” If they blink back, you’ve earned her undivided attention!

The Cat’s Eye’s Anatomy

A close up imagine of a ginger cat with dilated eyes

The Orbit:

The orbit is the bony socket or cavity that houses the eyeball. The orbit is a complex structure made up of many bones. Muscles, nerves, blood vessels, and structures that create and drain tears are all found in orbit.

The Sclera:

The sclera is the white layer of the skin. This is the eye’s comparatively sturdy outer layer. 

The Conjunctiva:

The conjunctiva, a thin membrane situated at the front of the eye, protects it. The conjunctiva covers the eyelid inside and extends to the edge of the cornea.

The Cornea:

 The cornea is a transparent dome on the front of the eye that allows light to pass through. The cornea covers the front of the eye and aids in light on the retina in the back. 

The Iris:

The iris is the light, circular part of the eye. It adjusts the amount of light that reaches the eye through dilation or contraction of the pupil. The pupil is a dark spot in the centre of the eye. The circular sphincter muscle controls the pupil. When the atmosphere is dim, the pupil expands to let more light in; when the environment is bright, the pupil contracts to allow less light.

The Lens:

The lens, which is located behind the iris, changes shape to focus light onto the eye. The lens thickens as small muscles (ciliary muscles) contract, allowing the lens to focus on nearby objects. These lens changes tend to be restricted in cats. 

As the lens focuses on distant points, the ciliary muscles relax, causing the lens to become thinner. The cells that perceive light are found in the retina (photoreceptors). 

Cones & Rods: 

Cones and rods are the two primary forms of photoreceptors. Cone cells have exceptional visual acuity and binocular vision in cats, enabling them to measure speed and distance exceptionally well, which helped them survive as hunters.

 Even though cone cells are also involved in colour vision, it is unknown if cats can see colours.

 Rod cells, which are excellent at collecting dim light, are abundant in cats. 

Cats can see six times better in low light than humans, giving rise to the urban legend that cats can see in the dark. 

The Tapetum:

The tapetum lucidum, a reflective coating on cats’ eyes, magnifies incoming light and gives their eyes a distinctive blue or greenish glint at night.

The Centralis:

The most vulnerable region of the retina in cats is known as the area centralis. Thousands of tightly packed photoreceptors render visual images sharp in this region. A nerve fibre connects each photoreceptor. 

The Optic Nerve:

The optic nerve comprises all of the nerve fibres packed together. The picture is converted into electrical impulses by photoreceptors in the retina, transported to the brain by the optic nerve.

The Eyelids:

The upper and lower eyelids are thin skin folds covering the eye and blinking reflexively to shield it. Blinking also tends to disperse tears across the eye’s surface, keeping it moist and removing tiny particles.

 Cats’ eyes are protected by the same eyelids that humans have and the nictitating membrane, also known as the third eyelid. This extra eyelid is a whitish pink colour located in the inside corner of the eye, beneath the other eyelids (near the nose). As necessary to shield the eyeball from scratches (for example, when travelling through brush) or in response to inflammation, the third eyelid extends up.


Eyes must be kept moist to work correctly. Tears have this much-needed moisture. Tears are made up of three components: water, oil, and mucus. Lacrimal glands produce the watery part of tears. They’re on the top of each eye’s outer edge. Glands also aid in forming the watery portion of tears in the third eyelid. 


Mucous glands produce mucus in the conjunctiva (called goblet cells). Meibomian glands produce the fatty/oily part of the eyelids. Water, oil, and mucus combine to form a thicker, more protective tear that takes longer to evaporate.

Nasolacrimal Ducts:

 Tears from each eye stream through the nose through the Nasolacrimal ducts. Each duct has an opening near the nose at the edge of the upper and lower eyelids.

What Health Conditions Cause The Dilation Of A Cats Pupil?

A brown cat crouching with bright blue eyes that are dilated.

Anisocoria is a health issue that causes large pupils in cats.

Compare your cat’s left and right eyes. Are the two pupils the same? Anisocoria is a condition that can make a difference. Technically, this is a symptom rather than a disease. Retinal disease, feline leukaemia, cancer, or an accident or eye ulcer may all cause it. The injury doesn’t need to be recent. Anisocoria may also be caused by scar tissue.

You might also note unusual colour variations in the rest of her skin. She can rub her eyes excessively or appear lazy, depending on the cause. A trip to the veterinarian is in order, and it should be done as soon as possible.

The pupil is an elliptical opening in the centre of the iris in cats that allows light to pass through the eyes to the retina. The amount of light that reaches the eyes causes the pupil to constrict or dilate (enlarge), with both pupils usually dilating in dim light and constricting in bright sunlight.

What is Anisocoria, and How Does it Affect Your Cat?

Anisocoria refers to a disorder in which one of the cat’s pupils is larger than the other. In some cases, the abnormal pupil will be the smaller ones, and in others, the irregular pupil will be the larger one.

What is the Causes of Anisocoria In Cats?

Since anisocoria is a symptom of a disease or disorder, there are many possible causes, including:

  • Corneal injuries, such as ulcers.
  • Horner’s syndrome is caused by a disease or damage to the brain or the nerves that run to the affected eye.
  • Glaucoma, a condition characterized by a rise in intraocular pressure (the pupil in the affected eye will be dilated).
  • Uveitis or inflammation of the eye’s interior (the pupil in the affected eye will usually be constricted).
  • Retinal disease is a condition that affects the eyes.
  • The development of scar tissue between the iris and the lens (known as posterior synechia), a disorder that may occur during uveitis.
  • Iris atrophy (a reduction in the amount of tissue in the iris) is a degenerative change that occurs as people age.
  • Iris tissue that does not grow correctly due to a congenital disability.
  • Cancer in the eye that has been affected.
  • Spastic pupil syndrome is a condition that can be caused by infection with the feline leukaemia virus.
  • Other infectious diseases including feline immunodeficiency virus (FIV) or toxoplasmosis.

If your cat develops anisocoria unexpectedly, you should treat it as an emergency and seek medical treatment as soon as possible to reduce the risk of permanent vision damage.

What Other Are The Other Symptoms Of Anisocoria In Cats?

The pupil in one eye will be larger or smaller than the pupil in the other eye in all cases of anisocoria. That could be all you notice in some cases. In other cases, the white portion of the affected eye may be swollen, the cornea (the outer surface of the eye) may be blurry or bluish, there may be a discharge from the eye, the affected eyelid may be droopy, the cat may be squinting or rubbing its eye, or the cat may be fewer active than average, depending on the underlying cause.

How Can You Figure Out What’s Causing Anisocoria In Cats?

A close up imagine of a grey cats dilated eye

Your vet-doc will begin by performing a physical examination on your cat, which will include a thorough examination of the eye’s structures. Your veterinarian may conduct additional, more precise testing based on these preliminary findings, such as measuring tear production and intra-eye pressure (pressure inside the eyes) for each eye. The cornea may be stained with fluorescein dye, and conjunctival scrapings or biopsies may be taken and sent to a medical laboratory for specialized examination to search for underlying corneal injuries or ulcers. In addition, vets can do blood tests to see whether a systemic disease like feline leukaemia causes the problem.

Your veterinarian may refer you to a pet ophthalmologist for additional diagnostic testing in some cases.

What Is The Treatment For Anisocoria In Cats?

Anisocoria care depends entirely on the disorder’s underlying cause, with personalized treatment adapted to the diagnosis. Your veterinarian will go through the best care options for your cat’s specific situation.

Cat Eyes and Hypertension

Hypertension (also recognized as high blood pressure) is a common physiological cause of dilated pupils. High blood pressure may be the result of a primary or secondary issue.

It’s secondary, which means some ailment or disease brings it about. For example, hypertension is a condition that can be caused by hyperthyroidism or kidney failure. As the first step toward a diagnosis, your veterinarian can shine a light into your cat’s eyes to see how her pupils respond.

If your cat has high blood pressure, she would most likely show other signs as well. For example, she may not be grooming herself as meticulously as she once was, or she may have gained or lost a few pounds. Another symptom is a loss of interest in food or drink.

Cat Pupil and Dysautonomia

Dysautonomia, also known as Key-Gaskell Syndrome, can affect cats with round pupils. This is due to your cat’s automatic nervous system, or ANS, which is in charge of all the physiological functions that your cat cannot regulate on its own, such as appetite and lack of it, heart rate, blood pressure, respiration, and pupil dilation.

If dysautonomia is the cause of her dilated pupils, you can note other dysautonomia symptoms as well. The most noticeable are problems urinating or defecating, as well as diarrhoea. In addition, her reflexes could be sluggish, and her nose could be unusually dry to the touch. Vomiting, as well as weight loss, coughing, and lethargy, are all symptoms. You can take your cat to the doctor as soon as possible if it has round pupils.

Veterinary Treatment for Dilated Pupils

Blood and urine tests can tell your veterinarian a lot, whatever the physiological cause of your cat’s big eyes. If your feline’s hypertension is exacerbated by something else, your doctor will treat the underlying disorder, likely extending her life, all because you found something odd in her eyes. Veterinarians can use traditional medicine to treat and monitor primary hypertension.

Anisocoria necessitates urgent medical attention due to the seriousness of the underlying condition. Your veterinarian would need to investigate, run some tests, narrow down the source, and treat the cause rather than the symptom once more. If your cat has lost its sight, it is usually irreversible, but several blind cats manage to get around just fine.

Even if your cat isn’t displaying any other symptoms but still walks around with dilated pupils, you should get the situation checked out. Constant dilation almost always suggests an underlying medical condition. On the other hand, dilation is usually just a by-product of a cat’s exciting life.

Of course, your feline’s often dilated pupils may be due to his personality, but you won’t know for sure until your veterinarian tells you.

Conclusion: Dilated Pupils in Felines

You know what your cat’s slow blink means: “I’m in love with you. I’m satisfied. Right now, I’m in a good mood.” But that’s just body language; physical factors like pupil widening or narrowing may also impact parts of her eyes.

The dark spots in the centre of her skin, technically in the middle of her irises, are her pupils. The most prevalent cause of a transition is the light of her surroundings, which is nothing to be concerned about. When there is a lot of light, her pupils will shrink, and when light is scarce, they should dilate or expand. While other factors can trigger changes in your cat’s pupils, it’s a perfectly normal biological reaction.


Rochelle is a self-claimed crazy cat lady and proud cat mum to Owlie! She has owned, rescued, and fostered cats throughout her whole life. Rochelle created Cats On My Mind as a hub for likeminded cat parents to get all the information they will ever need to give their fur babies their best life!

Leave a Reply

Your email address will not be published.

Recent Posts