Main causes of dilated pupils in cats


In addition to body language, cats use their eyes to communicate with us, other cats and animals of different species. For many, the look of a feline is one of the most mysterious due to the characteristic shape of its pupils, but what happens when they are completely round? In general, the pupils of cats usually resemble a vertical line, not a circle, so it is not surprising that when witnessing this change the tutors are alarmed. In this Animal Expert article we will talk about this and explain why your cat has very dilated pupils, keep reading!

Meaning of cat pupils

Over the years the domestic cat has been evolving and adapting some of its natural habits, and an example of this is its hunting preference. Due to the dangers that lurked them, the ancestors of the current cats were nocturnal animals that took advantage of the darkness of the night to feed and, at the same time, protect themselves from possible predators. This was possible thanks to the anatomy of his eyes, which gives this animal a excellent night vision. For this, the feline dilates the pupil as much as possible in order to favor the entrance of the greatest amount of light. In addition, in the eyes there is a tissue called tapetum lucidum that, in summary, allows to absorb and retain the light before reaching the retina, a fact that guarantees a much sharper vision at night.

During the day, the cat contracts the pupil and keeps it more or less closed depending on the amount of light there is. Thus, in general, we find the pupils of cats in three different ways:

  • Vertical pupil. It is contracted to avoid excessive light entry, otherwise the animal would be completely dazzled.
  • Elliptical pupil. It is partially dilated.
  • Round pupil. It happens when the cat's pupil is fully dilated, mainly in low-light spaces or hours.

However, the entrance or not of the light is not the only reason that leads the cat to contract or dilate its pupils, since in many cases it does so as a reflex act that shows its mood or health. Here are these causes.

Why does my cat have round pupils?

Once the function of the pupils has been explained in terms of the entry of light, something totally natural and characteristic of most animals, it is important to highlight that the dilation of the pupils may also be due to other factors. Thus, the answers to why your cat has dilated pupils are numerous and can be related to situations or reactions to health problems. Focusing on those causes related to emotions and feelings, round pupils in cats express:

  • Excitement: when the animal is very excited and nervous, for example, during a game session, it is common to see it with round or elliptical pupils. However, arousal does not always happen because of positive stimuli, since it can also be caused by stress or anxiety.
  • Satisfaction: In situations that produce happiness, the cat also dilates its pupils as a reflex act. An example may be when we fill your food bowl.
  • Fear: the cat has dilated pupils and wide eyes. This is a clear sign of fear and fear, which can be caused by a change, a loud noise, a situation, etc.
  • Aggressiveness: Cats dilate their pupils when they stare at their prey and get ready to attack, so if you look at yours in a similar attitude, they feel threatened and think to defend themselves.

Although some of the causes that explain why a cat has round pupils are positive, it is important to note that this it's not the usual way. In any case the dilation indicates that the animal is not relaxed, and if it occurs because he is playing or practicing some activity good for him, we should not worry, but if we observe his dilated pupils for much of the day we should start to think that the state Our cat's not the right one. It is possible that the animal is stressed by something, does not feel comfortable or safe, and it is our duty to find the reason that is disturbing it to treat it and restore emotional stability. To do this, we recommend visiting the article "Things that stress cats".

On the other hand, it is important to highlight that each cat is a world and can develop their own forms of communication, so that dilated pupils are not always a cause for alertness. By this we do not mean that we should not give the importance it deserves, but that it is essential to know our feline, its character, behavior and reactions to learn to identify an alert signal. Likewise, there are breeds of cats with a predisposition to show elliptical or dilated pupils without this being an underlying problem, such as the British shorthair cat.

Cat with dilated pupils due to health problems

There are certain pathologies and conditions that show pupil dilation in their symptoms, so if the light in the environment is normal, there are no stressors or stimulants but, even so, the cat has round pupils, it is time of thinking about your state of health, especially if you are elderly. The most common conditions and diseases that present the pupil dilation as a symptom They are:

  • Glaucoma
  • Uveitis
  • Renal insufficiency
  • Hypoglycemia
  • Feline Leukemia Virus (FelV)
  • Some types of cancer
  • Poisoning
  • Head trauma
  • Eye discomfort or injury
  • Anisocoria

In the following sections we will place special emphasis on some of these problems that also help us understand why a cat has dilated pupils and does not move.

Anisocoria in cats: one pupil larger than the other

Anisocoria in cats is the condition by which an animal presents the unequal pupils, so that one of them is more or less dilated than the other. This problem not only affects cats, since it can also occur in other animals, including humans. In certain situations this difference may be common, however, when the condition becomes permanent, it is not normal and we must act.

To know if the cat suffers from this problem, we will look at the most common signs. In addition to the obvious asymmetry of the pupils, another symptom of anisocoria in cats has to do with the obvious eye discomfort, so it is common to see the affected animal scratching your eyes often and in different ways. Also, in most cases, another sign present in the anisocoria is the bluish coloration of the eyes, which shows them opaque and / or red. It is also possible to observe the presence of legañas or abundant secretions, which do not allow to open the eye normally. All these symptoms can impair the vision of the animal, so it is likely that it will collide with objects or furniture, that it walks weird or disoriented. Apathy and decay usually appear as a result of general malaise.

The anisocoria is a symptom It can develop as a result of other diseases or eye problems, such as feline leukemia, corneal ulcers or uveitis. Therefore, if your cat has dilated pupils asymmetrically, you should go to the veterinarian to find the underlying cause, since the treatment will depend on it.

Dilated pupils in cats due to glaucoma and other eye diseases

He glaucoma in cats It is a disease that involves increasing the pressure of the fluid that is inside the eye (aqueous humor). In the eyes of cats, and in ours, there are drainage channels that, if blocked, cause the aqueous humor to accumulate and, therefore, the intraocular pressure increases, causing glaucoma and other problems derived from it, such as blindness.

However, glaucoma is not an eye condition that can cause dilation in the pupils of cats. Likewise, this pathology can also appear as a consequence of another, so it is essential to review all eye problems that round pupils may have as a symptom:

  • Retinal detachment
  • Uveitis
  • Progressive retinal atrophy
  • Optic nerve disorders
  • Corneal injury
  • Eye tumor
  • waterfalls

Cats with dilated pupils due to kidney failure

As occurs in cases of glaucoma or anisocoria, the elderly cats They are the most likely to suffer from kidney failure. However, it is also possible to observe this pathology in younger cats, so we should not rule it out if the symptoms coincide. Although it may be strange to relate renal failure to pupil dilation, the truth is that there is a good justification for this. When a cat suffers from kidney failure, he also suffers from hypertension which, in turn, causes some eye problems such as bleeding, retinal detachment, blindness, etc. For this reason, the cat can dilate its pupils and turn this sign into another symptom of the disease.

In addition to eye problems and pupil dilation, the symptoms of renal failure in cats that can alert them of their presence are the following:

  • Apathy
  • Loss of appetite
  • Weightloss
  • Polydipsia and polyuria (drink and urinate a lot)
  • Vomiting
  • Diarrhea
  • Excessive hair loss
  • Dehydration
  • Pale mucous membranes

Yes your cat has dilated pupils and does not move, this may be the cause. Renal insufficiency should be treated immediately since it is a serious pathology that can end the life of the animal. For more information, check out our article "Kidney Failure in Cats - Symptoms and Treatment" and check with your veterinarian, especially if your pussy is over 7-8 years old and has one or more of the symptoms mentioned.

Tips to clean a cat's eyes

Although we have seen that the causes that explain why a cat has dilated pupils are many and do not necessarily imply a lack of cleanliness, it is always recommended maintain good hygiene of this part of the body to avoid irritation or problems caused by dirt. Here are some tips:

  • If the cat produces many litters, they should be removed every morning with a sterile gauze and physiological serum or chamomile failing.
  • It is good to set one cleaning routine of the most delicate areas, such as eyes and ears, from puppies. For adopted cats, this point is also important, always little by little and through positive reinforcement.
  • If the hair around the eyes is too long, it should be trimmed to prevent it from penetrating the eyes and causing an injury.
  • If the cat has ocular discharge, inflammation, redness or excessive itching, it should be taken as soon as possible to the veterinarian.

In our article "How to clean the eyes of a cat?" We detail all the necessary material for your hygiene, steps to follow and recommendations.


If you want to read more articles similar to Why does my cat have dilated pupils?, we recommend you go to our Eye Problems section.

Characteristics of cat pupils

The pupils of any animal can be made smaller in bright conditions, something known as pupillary myosis, or they may dilate if there is little in order to capture as much light as possible, what is called mydriasis of the pupil. In the case of the cat, in addition, we have to talk about the tapetum lucidum, which is a tissue that is especially useful in low light conditions as it reflects it, however small.

In addition, feline pupils have another peculiarity: they are vertical, straight or elliptical.

What does the shape of the pupils of cats mean?

It will depend on how they are:

  • Vertical straight: when there is excess light, the pupil is reduced as much as possible to avoid damage to the eye.
  • Vertical elliptical: is the normal position, when there is a cant> Why does my cat have dilated pupils?

A cat can have dilated pupils for different causes:

    Emotions: fear, aggressive> When to take it to the vet?

As we have seen, a cat can have dilated pupils for various reasons. But If apart from this we see that it presents other symptoms such as lumps, vomiting, loss of appetite, or others, it will be very important to take it to the veterinarian to tell us exactly what happens and how to treat it.

Thus, in case of doubt it will always be better to consult with a professional. The cat's health depends on it.


Depending on the amount of light there is, the pupils of the cats contract or dilate to let in more or less light, just the necessary to create an image in the retina. The hunting nature of cats makes their vision optimal in low light conditions: His eyes are prepared to hunt at night adapting to the darkness.

The pupil is enlarged to collect the maximum amount and allow it to penetrate the eye. In the same way, if there is excess light in the environment, your cat's pupil will contract. This is what is considered a particular condition of the pupil in response to a stimulus.

On the contrary, if we see that there are no light conditions to see dilated pupils in cats, we can talk about mydriasis, which is a symptom by which dilated pupils in cats are present due to situations of mood or stress, as well as some diseases. Let's see more details below.


If you notice that your cat has dilated pupils, it may be due to non-worrying causes such as light conditions in the environment, as we mentioned above.

But not everything is in the ambient light: some emotions they can cause dilated pupils in cats. If your cat feels fear, is excited, happy or suffers an episode of stress, his pupils will dilate. If you see his dilated pupils When it plays or we have to transport you for your veterinary visit, you should not worry.

In the same way, if we have administered a eye drops or have been anesthetized, dilated pupils in cats are predictable and not symptomatic of disease.


If none of the benign causes are affecting your cat, it is best that we go to the veterinarian since it can be one of these health problems:

Infection due to inflammation of the eye or uveitis. Inflammation occurs in the part of the uvea.

Glaucoma which causes greater eye strain. It can be derived from a stroke, from tumors or from an infection or inflammation.

Retina detached that can lead to blindness. A high tension can cause retinal detachment. Diabetes, hyperthyroidism or kidney failure cause high blood pressure.

Virus leukemia feline

Poisoning caused by natural toxins (plants) or some medications.

B1 deficit. The group of B vitamins is responsible for regulating the nervous system. This problem stems from a poor diet, so it is best to provide your cat with a certified product and specially formulated for your needs.


When dilated pupils in cats do not change when changing light stimuli, you will also have to be attentive to the mood and other behaviors of your cat. Go to your veterinarian for a review: it will be normal to have different blood and urine tests and tests to detect the possible health problem. Before the suspicion of neuronal problemsIt is also important that a specialist acts so that he can diagnose properly.

The body language of cats

Unlike dogs, cats usually do not cooperate for hunting or form cohesive groups. Cat colonies are much more informal than the hierarchical wolf pack. Cats have had no need to evolve their social rules to live in communities. They get together with other cats to cross, raise kittens, and in some social groups like cat colonies or houses with multiple cats. Feline language is complex and subtle, with at least twenty-five different visual cues used in sixteen combinations. Undoubtedly there are many others, even more subtle, that we are not able to recognize. Most cat owners learn to recognize at least some of the visual cues of their cats.


The position of a cat's head indicates several things. If the head is stretched forward, the cat is asking us to touch it, or to better see the facial expression of the person - or of another cat. It is a greeting message. During a conflict, a confident cat will raise its head, while an aggressive cat will lower it. A lower or submissive cat will also duck its head, in submission. However, a fearful and aggressive lower cat will also raise its head. To understand the message, you must look at the other end of the cat: its tail.

The tail

The tail is an important tool for communicating with other cats and other species (such as humans). It is very mobile, from side to side, up and down, with grace and majesty, quickly or slowly, or as a whip. It can be curled up in a cat that is sitting or sleeping, or if it is scared it can "inflate." A mother can also use it as a "toy" for her kittens.

The tail of the cat is an expression of how it feels. A tail up is a happy tail. The cat is saying "Look how happy I am!" The lower the tail, the lower the mood of that cat. An angry or scared cat will wear its tail between its paws.

When the cat is sitting quietly looking at something, and the tail moves slowly, the cat is focused on something.

If the cat waves its tail from side to side, it does not mean that it is happy to see you, but quite the opposite: it means that it is annoying and angry. This is when the cat could bite or scratch. The more they move it, the greater their anger, so treat this signal with caution.

If the cat moves its tail very smoothly it means that it is happy, and probably wanting to play.

A straight tail, vertically and rigidly, with the tip to the side, indicates that the cat is curious or interested in something.

A rigid tail, completely vertical, with the tip also right, is a demonstration of intense happiness. When he has his tail like that, you can be sure that your cat is happy to see you!

A rigid tail with the tip that shakes means that the cat is somewhat irritated, so caution!

An inflated and arched tail indicates that the cat is in a defensive position. Be careful, because a defense can easily become an attack.

A submissive tail looks a lot like an angry tail in its movement from one side to the other, but usually it is positioned lower than the angry tail.

The eyes

Humans like eye contact. Is friendly. For a cat, prolonged eye contact is a sign of "I'm seeing you," or even a threat. The typical case is when you receive the visit of several people, and the cat, inevitably, approaches that person who does not like cats. The "cat lovers" usually observe the cat, waiting for it to approach and then pet it. Those looks of strangers are, for the cat, menacing. However, the person who does not like cats does not pay attention, hoping that the cat does not bother them, and the cat does not feel threatened, comes to socialize with them.

Wide open eyes points out that the cat feels curious and happy.

Ajar eyes are an obvious sign that your cat is ready to sleep. However, if the eyes are ajar but your cat is fully awake, it could mean that your cat has some disease or infection.

Dilated pupils indicate that a cat is scared and about to become aggressive.

The various poses of the cat. Relaxed, aggressive, confident or fearful.


The cat's ears are extremely mobile. With between 20 and 30 muscles that control it, they can rotate 180º and move up and down. They can be pointed, or flat on the sides or back.

The ears of a cat that is happy are up and in constant motion, and turn in the direction of each sound they hear.

Scared or defensive cats flatten their ears to the side, as a sign of submission. Cats that are fighting also often show this behavior, to avoid injuries.

An angry cat shows its aggression by pointing its ears forward forming an angle.


Mustaches not only serve to measure the width of the places where the cat will pass, or the proximity of objects. They are also mobile and help determine the mood of the cat. In a relaxed state, you will see them slightly to the side.

A happy or curious cat has its whiskers fully extended. As the cat becomes more interested in something, the whiskers extend forward, until they are in front of the snout.

If the cat is afraid, irritated, or ill, its whiskers are pulled back along its cheeks.


Rarely a cat uses its mouth as a sign of aggression. A yawn may mean a non-threatening signal. A hiss with an open mouth demonstrates that the cat feels threatened and defensive. The grunts are emitted with the mouth barely open. Showing teeth is not like in dogs, it is the way in which the cat analyzes the aroma signals.

Other body signals

Purr. Most of the time it means they are happy. However, sometimes a cat purrs at the expectation that they will be happy, like when you are preparing the food, or when they know that you are going to caress them. Sometimes a cat purrs when it is afraid, or they are injured and in pain.

Quiet meow: Your cat can approach you, barely turn its head, open its mouth, and emit a tiny noise, almost like a hiccup. It's a cat's way of saying "Please!"

Rubbing: Sometimes a cat rubs against a person and wraps its tail around the legs. He is trying to know that person's temperament, and to know if he is friendly or not. It is a form of greeting. If a cat rubs against you with its body or the sides of its face, it is only marking its territory. However, if the cat rubs with its forehead or nose, it is a true sign of affection.

If you yell at a cat, and he knows he has done something wrong, they will defensively, as if giving up. This is a sign to let you know that he knows that you are angry.

If your cat is angry with you, they can turn around and leave, with their tail up, and shake one leg as if saying "I already had you, I'm leaving."

Final note

If your cat behaves strangely, it is very likely that he has some discomfort or illness. Watching it closely and learning to understand your cat's body language will not only bring you closer to your pet, but it can be helpful as an early warning of signs of illness. You could even save your cat's life.