Hepper is reader-supported. When you buy via links on our site, we may earn an affiliate commission at no cost to you. Learn more.

Why A Cat’s Pupils Get Big (Learn the Meaning of Cat Eyes)

Nicole Cosgrove Profile Picture

By Nicole Cosgrove

lynx point siamese_Kolander Art_Shutterstock

Cats can come off as standoffish and be hard to read. Like other animals and pets, body language is an essential part of communication. Apart from body language, cats also use their eyes to express themselves.

Unlike dogs, cats don’t have expressive faces, making it harder to tell the meaning behind their eyes. The non-verbal communication cues involve the tail and facial features. However, the cat pupils are critical because apart from responding to the light level in a room, they also give you a good sense of how your cat is feeling emotionally and physically.

In the complex world of feline body language, widened pupils say a lot. So let’s take a closer look at the meaning of cat eyes.

Why A Cat’s Pupils Get Big

chartreux cat eyes_LucasBouillon_Pixabay
Image Credit: LucasBouillon, Pixabay

The occasional dilation of cat eyes can result from emotional, environmental factors, or even age. On the other hand, some medical conditions contribute to constant dilation. It is normal for pupils to dilate and constrict to improve our vision.

Cats are naturally nocturnal, and their eyes are highly sensitive to light. Because of this, their pupils dilate dramatically. These characteristics make cats’ eyes appear large at night.

If your cat’s pupils dilate periodically and as the light around them changes, this is normal. However, if you notice your cat has large pupils that stay dilated all that time, it’s a cause for concern.

1. Better Vision

Pupils dilate due to the nature of their eyes. Like in humans, the pupils will dilate in the dark. The black circle in the middle of the eye controls how much light is allowed into the eye. In the dark, the pupil will widen to let more light in.

Cats can see much better in low light conditions, thanks to their pupils dilating and letting as much light into their eyes as possible. Because of this high sensitivity to light, your vet will use a bright light to test the eye function during medical check-ups. If the eye doesn’t constrict, this is a clear indication that there is an underlying problem.

chartreux cat in grass_Piqsels
Image Credit; Piqsels

2. Surprise or Fear

A cat’s pupils can widen out of surprise and fear. So, if you notice the pupils get suddenly dilated, it could indicate they got surprised or are scared. This could be from a sudden appearance of a visitor that they were not expecting, a loud noise, or the sighting of another pet outside.

Apart from the adrenaline rush, the pupils dilate until they settle down. Therefore, if you notice your cat is going through this, it’s better to leave them for a while until they realize they are in a safe place and settle down.

3. Excitement

Dilated pupils and big eyes are not always a sign of bad things. Your cat might just be excited about something.

Your pet might be happy because they got their favorite treat or are about to play with their favorite toys. Cat’s eyes dilate when they are playing because of the adrenaline pumping around their bodies.

4. Hunting in the Dark

When hunting prey, especially at night, cats need to be alert and fearless. The adrenaline rush also makes their pupils dilate.

As natural hunters, they have wide pupils and large eye lenses that let them collect information about their surroundings. These characteristics kick into action at night, even more, widening their eyes to allow better vision.

american shorthair cat_Piqsels
Image Credit: Piqsels

5. Defensiveness

If your feline friend has large pupils, they might be going into a defense mood. If they feel threatened by another animal or human being, they’ll tend to become aggressive, which can lead to scratching and biting.

The “flight or fight” response is also prominent during hunting sessions. Therefore, if you feel your cat is in defensive mode, it’s best to also give it time to cool off.

6. Anxiety

Wide cat pupils also indicate anxiety. When your cat is tense, you’ll notice one or all of these signs, hunched back, tense tail on its side, lowered head, and huge eyes. For instance, this can happen when your pet is nervous at the vet’s office or during heavy thunderstorms.

However, if your cat is diagnosed with chronic anxiety disorders, their eyes might be constantly dilated because they are constantly on edge. If your pet gets exposed to long periods of high stress, you’ll need to ease them into a new environment where they feel safer in the house.

chartreux cat_LucasBouillon _Pixabaychartreux cat_LucasBouillon _Pixabay
Image Credit: LucasBouillon, Pixabay

Medical Conditions That Cause Wide Dilated Pupils

While most of the eye dilation in your cat happens on a typically normal day, it might be due to a medical condition in severe cases. It’s normal for the eyes to be in a neutral state where they are neither overly constricted nor over dilated.

Here are some of the common reasons why your cat’s eyes are always dilated.


cat and vet. _Maria Sbytova_Shutterstock
Image Credit: Maria Sbytova, Shutterstock

Hypertension in cats is one of the leading causes of dilated pupils. Older and overweight cats are highly prone to this condition and will have a blood pressure that’s greater than 160mm Hg.

Vets diagnose hypertension by observing your pet’s eyes. If they don’t constrict under bright light, it could be a sign of high blood pressure.

This medical condition needs to get treated early enough; otherwise, it can cause the retina to detach and lead to blindness if left untreated. Feline hypertension also results as a secondary medical condition such as kidney failure. The vet will recommend medication depending on the underlying problem.

Widened eyes are also a side effect of some medications. Therefore, the pupils might remain dilated throughout the treatment period. As long as the medicine is working, there’s no cause for concern.


This condition occurs when your cat’s eye pupils are in different sizes. In this case, only one eye is constantly dilated. Anisocoria is a symptom of other medical conditions. It can result from corneal ulcers, glaucoma, retinal diseases, cancer in the eye, head trauma, or exposure to chemicals and toxins.

Because of this, the treatment of this medical condition will depend on the underlying cause. For example, if the cat has glaucoma or a corneal ulcer, it’ll experience squinting or rapid blinking.

In addition, they could have bulging and bloodshot eyes that come with intense pain. For toxicity, the cat might experience loss in appetite, nausea, and vomiting.

No matter the cause of the anisocoria, it’s critical to visit the vet for medical advice. They might recommend a veterinary ophthalmologist for further diagnostic testing. Full recovery will depend on the extent of the underlying condition.


chartreux cat brown_LucasBouillon_Pixabay
Image credit: LucasBouillon, Pixabay

Cats that are losing their vision will have constantly dilated eyes. These large pupils are an attempt to let in as much light as possible to help improve their vision. Apart from the big eyes, your cat might be experiencing loss of vision if they constantly bump into objects or are clumsy around the house.

Old cats are more prone to blindness and loss of vision; therefore, they will most likely have constantly dilated pupils. Immediately you suspect your cat is losing their vision, take them to the vet to get treated.

The blindness could become permanent or could be temporary due to kidney diseases and other eye infections.

Feline Dysautonomia

siamese cat in grass_rihaij_Pixabay
Image Credit: rihaij, Pixabay

Feline Dysautobimia is a medical condition that affects your cat’s autonomic nervous system (ANS). This system is essential because it controls all the automatic functions in the body, such as respiration, heart rate, arousal, digestion, blood pressure, and pupil dilation.

If the ANS is not working properly, the pupils will not dilate automatically or respond to light. This condition mostly affects younger cats; therefore, you need to observe the kittens to ensure they get treatment early enough. It’s also very rare; therefore, consult with your vet first before starting any treatment.

Chronic Body Pain

siamese lynx point cat_Michel Bertolotti_Pixabay
Image Credit: Michel Bertolotti, Pixabay

As natural hunters, cats will always try to hide the fact that they are in pain. Therefore dilated pupils and widened eyes are one of the ways to know that your pet is suffering from bodily pain.

It might be hard to diagnose the source of the pain at home. Instead, schedule a trip to the vet who’s best qualified to diagnose and treat your pet.

Some of the most common conditions that cause pain include dental problems and arthritis. The vet will recommend painkillers and the proper therapy to keep your pet pain-free.

Ocular Tumors

maine coon cat_Michelle Raponi_Pixabay
Image Credit: Michelle Raponi, Pixabay

If your cat’s eyes can’t constrict, they might have tumors. Ocular tumors exhibit as dilated pupils due to intense pain, inflammation, or cloudy eyes. Unfortunately, glaucoma also occurs frequently in cats with eye tumors.

Although some of the tumors are not cancerous, it’s best to have them removed as soon as you can to prevent the tumor from spreading around the body. If the growth is not severe, it can get removed using a laser; however, the cat’s eye may have to get removed in severe cases. In this worst-case scenario, cats can adapt and live happily with only one eye.

Iris Atrophy

Iris atrophy is mostly associated with old cats. This age-related condition makes the colored part surrounding the pupil known as the iris become thin.

The iris is an essential part of the eye as it gives the eyes a beautiful color and helps the pupil contract and adjust to the light. When the muscle thins out, it becomes harder to constrict the pupil, and the eye remains wide.

This condition does not cause pain or long-term vision problems. However, your cat will become more sensitive to bright light. Despite this, it’s still vital to take your cat to the vet to rule out any other serious medical conditions such as hypertension, glaucoma, or blindness.

siamese cat in wild_Andreas Lischka_Pixabay
Image Credit: Andreas Lischka, Pixabay

Medications Side Effects

Cats have wide round eyes due to the medication they are on. Some painkillers cause the pupils to dilate as a side effect. The only way to determine whether this is the cause is by observing how your cat’s eyes behave after administering some medication.

In addition, the dilation can be a result of an overdose. If the dilation does not go down for extended periods when the cat is still on treatment, your vet can reduce the number of medications or switch to a milder pain killer. This condition is not dangerous as long as you observe your pet closely in consultation with the vet.

What Does It Mean When a Cat Has Split Pupils?

Cats can also have squinted eyes. Here are the reasons a cat’s pupils get contracted into a very slim vertical slit.


White persian cat II_Kadres_Pixabay
Image Credit:

A slit-eyed look in your feline buddy can indicate aggression. The cat will squint the eyes to protect its eyes from the potential claws of an opponent. If you lock eyes with the cat during this time, it might attack you.


Strong emotional arousal can range from anger, fear to pleasure. When your cat is going through these emotions, the pupils contract and become narrow slits. This can happen when your cat gets its favorite food and is getting ready to eat.


Squinted and half-closed eyes could also be a sign of trust and affection. When the cat does this, it means they are comfortable around you and feel relaxed enough to fall asleep.

Why Does It Mean When a Cat Stares?

persian cat_Pixabay
Image Credit: Pixabay

A cat’s stare can communicate what they are feeling. There are different types of cat stares depending on your cat’s emotions. So, let’s take a closer look.

Direct Stare

Cats that hold eye contact or stare you down do this to determine dominance. They’ll stare you down if they feel threatened or trying to intimidate you.

You can make the kitty more comfortable by breaking away from the staring and looking away. This reduces their level of anxiety.

When doing the same to other cats or animals, it’s a sign of dominance to try and keep other felines from coming close to its food, litter box, or marked territory.

Breaking Eye Contact

persians cat_lindarczyk_Pixabay
Image Credit: lindarczyk, Pixabay

A cat that stares for a few moments then breaks eye contact around you is comfortable. This shows they are okay with you around and don’t want to get aggressive.

Calm Stare

The calm stare is a sign of affection. Cats like watching over their human owners in the same way you keep an eye on them.

What Does It Mean When a Cat Has Slow Blinks?

Image Credit: redwineandyou, Shutterstock

Slow eye blinks are a means to express love and trust. Your cat’s eyes and lids will partially close or droop, and the cat will have a sleepy appearance. To return the affectionate feelings, you should meet your pet’s gaze and blink back.


Feline body language is so confusing to most cat owners. Because cats can’t express themselves verbally, the caretakers have to study their body language to detect any changes.

Cat eyes give away a lot of information about how a cat feels. In addition, veterinarians can use these eye changes to detect other underlying medical conditions.

Although eye pupils widen and constrict under normal situations when exposed to different amounts of light, it becomes concerning when the pupils stay constantly dilated. If your cat’s pupils are permanently dilated, it’s best to take them to a vet for a check-up. When the underlying medical conditions get treated early enough, you can save your pet from blindness.

Featured Image Credit: Kolander Art, Shutterstock

Related Articles

Further Reading

Vet Articles

Latest Vet Answers

The latest veterinarians' answers to questions from our database