Why Are My Cat’s Eyes Always Dilated?

Russell Cargill

Dilation of a cat’s pupil can be caused by many factors, some being normal physiological responses to the cat’s environment, and others being a result of some kind of disease or abnormality. 

If you have ever thought to yourself, “Why are my cat’s eyes always dilated?” it may be time to take a deeper look at your cat’s daily habits and environment to determine if something is causing abnormal dilation. 

Why Do Cat’s Eyes Dilate?

Cat’s eyes dilate for a variety of reasons, but the most common reason to see changes in pupil size is due to light changes. When there’s a bright light, the pupil will constrict, and when it’s dark outside, the pupil will dilate to let more light in.

By changing depending on light levels, cats can maintain great eyesight throughout different times of the day. It’s what makes them great hunters at night. 

Their eyes can also dilate based on mood or behavior changes. Sudden changes in the eyes should be seen as any other common body language change. This can be taken as a sign of aggression, fear, anxiety, or even excitement. As with any other body posture, however, it should always be considered within context. 

If you’re playing with your cat and its eyes dilate, this is likely a sign of excitement. If your cat is running from a dog and you notice a lot of dilation, this is likely out of fear. Always be sure to consider the environment your cat is in before jumping to any conclusions about why their eyes may be changing in a specific way.

However, if your cat has constant pupil dilation, this could be a sign of potential health problems like elevated blood pressure, also known as hypertension. 

Why Are My Cat’s Eyes Always Dilated?

If your cat has constantly dilated pupils, it’s a good idea to bring them to a veterinarian to check to make sure they have normal results on a blood test and that their blood pressure is at a healthy level. 

Loss Of Sight

Since the eyes dilate primarily to control the amount of light that comes in, if your cat has any trouble seeing, their eyes will likely always be dilated. This is the body’s way of attempting to see by bringing in as much light as possible. 

This could either indicate that they have some vision loss that they are trying to work through, or that they are completely blind. You can determine this both with your veterinarian or by doing common sight tests at home. By waving your hand on either side of their face, you will be able to see if they have any reaction to your motion.

Whether you can accurately determine your cat’s level of vision loss on your own or not, it’s imperative to bring him to your veterinarian to make sure no potentially harmful conditions are contributing to the problem, such as tumors or degenerative diseases. 

Tension And Anxiety

Cats that naturally have high levels of anxiety will show more constant dilation of the pupils as this physiological response comes with the fight or flight instinct. 

When a cat has increased stress hormones, its senses go into overdrive. Their ears stay more alert, and their eyes remain in a state that allows them to see anything that poses a threat to them, which happens to be the dilated state. 

If this seems to be a problem with your cat, it’s important to take it just as seriously as any other physical ailment as long-term anxiety can lead to further health problems like malnutrition. 

Take a look at the environment that your cat is in and observe if there’s anything inherently stressful. If you have another pet that shows aggression towards the cat, this could be a cause of chronic anxiety. If your cat does not have enough food or water, this puts stress on the body. Even a lot of exposure to loud noises can be a source of stress and insecurity. There are plenty of examples that you may be able to find in your own home.

If there are any stress-inducing situations you can alleviate for your cat, you may see a reduction in their anxiety. Keep in mind you can also get medication for your cat to reduce their stress; however, you should always consult your veterinarian before giving any new foods or medication to your pet. 


Similar to stress and anxiety, overstimulation can cause the fight or flight response in your cat. If you have a shy cat, this will be especially common as their tolerance for a busy environment may be lower. 

If you have a lot of children in your home that is constantly chasing or picking up the cat, it’s a good idea to create rules about how they play to reduce the stimulation the cat is receiving. 

By reducing any unnecessary stimulation, you will find that your cat can come out of the fight or flight response which may also help them to absorb more nutrients in their food, sleep better, and ease the tension they hold in their dilated pupils. 

Chronic Pain

As a way to avoid predation in the wild, cats have evolved to hide any physical pain they may be experiencing. Therefore, even if your cat has a severe injury or source of tension, they will try to take care of it themselves without drawing any attention towards it. 

One tell-tale sign that they have pain is through pupil dilation. If coupled with any increased aggression, especially when you’re handling them, or a loss in appetite, your cat could be indicating that it has a problem.

Other signs of pain include:

  • Reduced grooming
  • Lethargy 
  • Hiding or purposely avoiding human interaction

All of these signs are very cat-specific so look for major behavioral changes related to these areas of your cat’s life. If you think your cat is experiencing chronic pain, be sure to bring them to the veterinarian as soon as possible. 

Avoid giving any medication or painkillers without first consulting with a vet as many common painkillers are toxic for cats.

You can give aspirin in small doses when advised by your veterinarian but, never give your cat paracetamol as it’s highly toxic to their bodies and they can’t break it down. 

The result of this drug will not be pain management, but rather will shut down their liver, causing jaundice and swelling around their face and neck. This can also cause red blood cells to break down and start dying, causing hemoglobin to enter the urinary tract. This will ultimately kill your cat, so always only provide the pain medication prescribed by a veterinarian to your cat.

Toxicity And Poisoning

When given a substance that’s toxic to a cat’s body, the central nervous system is being attacked and therefore will show physical signs like face twitches, dilated pupils, and seizures.

It’s important to be aware of what can cause poisoning in cats to best be able to avoid your cat coming into contact with those items. Several foods and medications can cause toxicity, but even things like cleaning products can poison your cat. To reduce the chances of anything getting into your cat’s body, be sure to store all potential toxins in places that your cat cannot access. 

If your cat is an outdoor cat, be aware of the plants in your region that could pose a threat such as tomato plants

While cats will usually do a good job of avoiding anything harmful to them, some breeds don’t have the same instincts as others and therefore may accidentally come into contact with or eat something that isn’t good for them. 

If you think your cat has been in contact with a toxin and is showing the physical responses to poison, bring them to an emergency clinic right away! If action isn’t taken quickly, they can die or have long-term impacts from the poison. 


Hypertension, also known as high blood pressure, is known as any pressure reading above 160 mm Hg. While high blood pressure is often related to stress, this isn’t the case with felines. 

Cats develop hypertension usually as a result of kidney, heart, or thyroid abnormalities or disease. If you’re not sure if your cat is experiencing hypertension, the best way to test is to see if your cat has dilated pupils that don’t constrict when exposed to bright light. If they have normal vision, but no constricting, this may indicate an issue with their blood pressure. 

Other signs to look for include:

  • Blood in the chamber of the eye
  • Blindness
  • Detachedness of the pupil

All of the tell-tale signs here relate to the eyes, stressing the importance of paying close attention to the health of your cat’s eyes. 

Iris Atrophy

Iris atrophy can both inadvertently make your cat’s pupils look dilated, while also making it more challenging for the cat to restrict their pupils. Iris atrophy occurs in older cats as the iris, which is simply the muscle that aids in pupil dilation and contraction, starts to thin. 

While this can be seen by the colored part of the eye getting thinner, it can also make it look as though the pupil is getting larger. Although this can throw off the balance of the eye, with less muscle around the pupil it can also make it harder for the pupil to be controlled. 

This can make them more sensitive to bright light as they are less able to control their dilation and more serious side effects can be blindness and serious eye diseases like glaucoma. 


Although it’s one of the rarest diseases in cats, dysautonomia impacts the autonomic nervous system. This is the system that functions without us consciously having to think about it. Other examples of these functions include our heart beating, or our stomachs digesting. 

If the autonomic nervous system is stunted, these automatic functions become more difficult. In this case, the eyes of your cat will often stay dilated. Keep in mind this commonly affects younger cats and is life-threatening if not treated immediately.

The only treatment for this is a medication that must be given by your veterinarian. Some other signs that can help you determine if this is an issue include:

  • Loss of bladder control
  • Vomiting
  • Loss of spinal reflexes
  • Loss of respiratory regulation
  • Abnormal muscle loss

These are very urgent problems if observed in your cat and should be tended to right away. 

Eye Diseases, Ulcers, And Infections

If your cat has any eye diseases, in addition to pupil dilation, there are a few things that you may notice. Ulcers and tumors are often accompanied by eye inflammation and cloudiness. You may notice redness in the eyes or what looks like severe irritation. 

If you see cloudiness, this can also be a concern for glaucoma which isn’t an uncommon eye disease for cats. Remember that inflammation, discharge, and irritation can also simply be the result of an infection or allergy. Infections can easily be caused by a small scratch on the eye or getting a piece of matter into the eyeball. 

These can be easily treated with medicated drops. It’s always best to bring your cat to the vet when these kinds of symptoms present themselves as it can be difficult to determine what the cause is. 

If the eye is clear, the infection will likely go away on its own. If there’s a tumor, it can sometimes be removed with a laser and tested to see if it’s cancerous. Worst case, sometimes with tumors or other eye diseases, the eye must be removed to prevent further irritation or pain. 

If this is the case for your cat, don’t worry because cats are extremely adaptable animals and can maintain the same lifestyle with only one eye. 

Only One of My Cat’s Eyes Is Dilated

If you’re noticing that just one of your cat’s eyes is constantly dilated, or just that you’re seeing a big difference between the size of the two pupils, this may be a sign that your cat has a very different issue than those outlined above. 

Feline Spastic Pupil Syndrome

If only one pupil is constantly dilated, this can be a sign of anisocoria, a condition in which your cat’s pupils are two different sizes. The condition leading to this development is feline leukemia, which causes spastic pupil syndrome. 

If you’re noticing a big difference in the size of your cat’s pupils, this is the first thing to check with your veterinarian. Keep in mind that this condition can come and go, just as it can switch eyes.

A few other conditions that can lead to anisocoria include iris atrophy, glaucoma, and any ocular cancer. While the anisocoria itself will not cause major harm to your cat, the underlying condition that it’s being caused by may be harmful, so get them to your vet right away. 

This condition can also present itself as one pupil being very tiny while the other looks seemingly normal. So don’t be attached to looking for pupil dilation with this one, simply look for pupil differences. 

Why Are My Cat’s Eyes Sometimes Dilated?

Occasional dilation in your cat’s eyes is normal! All animals’ eyes dilate so that they can see properly. Therefore, it’s more abnormal if you never see your cat’s eyes dilate or contract. 

The most common reason you will find in a healthy cat is the changes in light. If you’re ever up in the middle of the night and spot your cat, their pupils are likely majorly dilated as a result of their environment being dark. The darker it is, the more the pupil will expand to offer better night vision.

If your cat hears loud noises like fireworks, their eyes dilate because they are scared or nervous. The same will go for when you play with them, as they are showing their excitement.

Dilation of the eyes is a way for a cat to focus on what’s going on around them and therefore can be in response to something positive or negative. 

If you never see your cat’s eyes dilate, you should take them to the veterinarian as they may have a problem physiologically or with their vision. 

Are Your Cat’s Eyes Really Always Dilated?

The following is very important is to think about when you see your cat’s eyes.

If to you they are always dilated but you’re only home when it’s dark out or you’re only looking at their eyes while you play with them, you may think the dilation is constant when in fact it isn’t.

Therefore, before jumping to the conclusion that your cat may have an ocular problem, make an effort to observe them at different times of the day to be sure you’re not seeing their eyes change. 


If you work all day and your cat is alone, they will likely experience dilated pupils when you return because they are excited to play and have company. If you have a very affectionate and family-oriented cat, you may find that their eyes look dilated more often because they are often excited and in a heightened mood. 

This is simply the reaction they have to arousal and stimulation, not being indicative of any kind of retinal disease or abnormality. 

Enhanced Vision

Alternatively, cats have amazing vision and heightened senses. Throughout their day there will be times when their pupils dilate a lot more, generally being a sign that they are highly focused on something.

In this case, be sure to keep a close eye on your cat’s health to make sure you don’t see any other abnormal symptoms that may be cause for concern. If you don’t see any other problems with their mood, reflexes, eyes, or stool, they are likely dilating due to the need for enhanced vision. 


While having frequent dilation of the eyes isn’t abnormal in cats, it can be an indicator of a deeper problem. If you’re noticing anything off about your cat, be sure to bring them to the veterinarian as soon as possible since the smallest of symptoms, like eye changes, can be telling of something much more serious. 

In this case, always keep track of the symptoms you’re seeing as well as the frequency they are occurring. By collecting this information, you will better be able to assist your veterinarian in properly treating your cat. 

Frequently Asked Questions

Cat you give a dog or cat aspirin?

As a general rule, it isn’t recommended to give your pet any medication without first clearing it with your veterinarian. Aspirin when given in high doses can cause issues such as gastric irritation, respiratory problems, and hepatitis. This is because cats cannot break down Aspirin in the same way humans can due to their metabolic rate. 

What is the black discharge coming out of my cat’s eye? It looks like blood.

Much like humans, cats get discharge from their eyes, especially when sleeping. However, their tears often have pigmentation which, when exposed to sunlight, can turn them black. This can create a goop in the corner of the eye that looks black and almost like blood. If you see this, don’t worry, it’s simply your cat’s eye cleaning itself.

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