It is usual for pupils – the black part in the center of our eyes – to dilate and constrict to improve our vision.
At night when it’s dark, they dilate to let light in. When it’s light, they constrict and become smaller in size, allowing us to always have the optimal amount of light for the best vision possible.
Animals’ eyes work the same way, including cats’ eyes. But what if your cat’s eyes are always dilated? Unfortunately, constant pupil dilation is not a good sign! It is commonly a sign of hypertension but could also indicate that they are blind, are experiencing chronic pain, or have another underlying health condition.
I run through all these reasons for dilated pupils and more in this article, so see which you think applies. Always get your cat to the vet if you notice they have big round pupils all the time, though. Cats rely on their vision, and unchecked eye conditions can lead to blindness.
Why Are My Cat’s Eyes Always Dilated?
It is normal for cats’ eyes to dilate when light conditions change or to express fear, anxiety, or excitement. However, it is a cause of concern if you see your cat’s eyes always dilated.
Here are the most common explanations for why cats’ eyes are always dilated. See which you think applies but remember that I am not a vet! Always take your cat for a checkup if you notice anything funny with their eyes. It isn’t worth risking leaving a potential medical condition unchecked.
High blood pressure, also called hypertension, is when cats’ blood pressure exceeds 160mm Hg. Hypertension is the most common reason why your cat’s eyes are always dilated. Your cat’s pupils will be big and round all the time when they have high blood pressure, even when the vet shines a bright light in their eyes.
It can be challenging for vets to diagnose hypertension, and these visual abnormalities are usually the first sign that something is wrong. You must take your cat to the vet if you think they could have high blood pressure, as if left untreated, it can cause the retina to detach, resulting in blindness.
Feline hypertension can be related to several factors, including kidney disease, thyroid problems, or heart disease, so they may also need treatment for these underlying conditions. The condition is also more common in older cats or those that are overweight or obese.
The treatment prescribed by your vet will vary depending on the cause of feline hypertension, but it is usually treated with an oral medication that addresses the underlying conditions.
If your cat always has dilated pupils even after treatment, don’t worry! One of the drugs used to treat hypertension can cause pupil dilation as a side effect. As long as you keep going to the vets to check that their medication is still working regularly, this is nothing to worry about.
2. Blindness or Loss of Vision
If your cat always has dilated pupils, it could indicate blindness. Cats struggling to see will have large pupils to let as much light into their eyes as possible to aid their vision. This is their body’s way of compensating for their deteriorating sense of sight.
Cats’ eyes do deteriorate with age. Unfortunately, there is little we can do to prevent age-associated blindness other than asking for veterinary advice at the first sign of eye-related issues.
However, cats can also develop temporary blindness due to kidney diseases, feline herpesvirus, or severe eye infections. These conditions often cause a sudden loss of vision and require an urgent trip to the vet. Below are some common signs aside from cats having round pupils that could suggest blindness:
- Bumping into objects and acting clumsy
- Being overly cautious when jumping or climbing
- Acting more startled than normal
- Confusion and disorientation
Many ocular issues – such as a detached retina – can be successfully treated by your vet. On the other hand, there is no treatment for cats that are permanently blind. Still, it is good to get a firm diagnosis from your vet. You can then make any necessary adjustments to make your cat’s life as simple as possible.
3. Anxiety Disorder
It is normal for cats’ eyes to dilate in response to fear. The pupil dilation lets more light into their eyes, improves their vision, and gives cats the best chance of escaping danger.
If your cat’s eyes are constantly dilated because of fear, it may suffer from chronic anxiety or stress. Chronic anxiety can be caused by all kinds of things, such as:
- Chronic pain or illness that is causing permanent discomfort
- A complete change of environment, such as moving home
- Traumatic experiences earlier on in life
- Lack of socialization when in kittenhood
- A history of abuse or neglect earlier on in life
- Long-term stressors in their environment, such as another pet they constantly have to compete with
Sustained periods of high stress can trigger several other problems, including aggression or a loss of appetite. Therefore, you must try to understand why your cat is permanently stressed.
Start by assessing whether there have been changes to their usual environment or routine to identify the trigger. If you can remove the trigger, do so – you should notice your cat’s eyes are no longer dilated after they’ve calmed down.
Sometimes, removing the trigger isn’t possible! Instead, make adjustments such as adding plenty of hiding places and maintaining a strict routine to help them deal with the stress. Some cats also respond well to calming scents and pheromones. Speak to your vet if you can’t seem to calm your cat down by improving its environment.
4. Chronic Pain
Cats’ pupils dilate when they are in pain. Therefore, the reason your cat’s pupils are so big constantly could be chronic pain. Cats instinctively try to hide feelings of pain as it makes them appear vulnerable. Always dilated pupils are one of the only giveaways!
Alongside dilated eyes, your cat may also exhibit several other symptoms if chronic pain is the cause. Watch out for all of the following signs:
- Loss of appetite
- More aggressive towards you and other animals
- Increased lethargy and overall weakness
- Being more withdrawn and less tolerant of people
- A disinterest in grooming or grooming excessively
To determine the source of your cat’s pain, it is best to take a trip to the vet. They will then be able to diagnose what is causing your cat continual discomfort. Some of the most common causes of pain in cats include arthritis, dental disease, or soft tissue injury.
5. Feline Dysautonomia
Although extremely rare, your cat may suffer from feline dysautonomia (also called Key-Gaskell Syndrome). Unlike many other conditions on this list, it typically affects young cats. If your kitten’s eyes are always dilated, Key-Gaskell Syndrome could be the culprit.
Dysautonomia affects your cat’s autonomic nervous system (ANS). The ANS is what controls all automatic bodily functions, such as heart rate, respiration, digestion, urination, arousal, blood pressure, and pupil dilation. It essentially controls every essential bodily function that does not require conscious thought.
Cats with Key-Gaskell syndrome cannot regulate these functions, so their eyes are constantly dilated. As the autonomic nervous system extends to all areas of your cat’s body, symptoms are widespread. Other signs of the condition include:
- Upper respiratory problems
- Constipation, diarrhea, and vomiting
- Incontinence or extremely slow and painful urination
- A slow heart rate (<120 beats per minute)
- Swollen esophagus, abdomen, and bladder
- Lack of appetite and weight loss
- Droopy eyelids and protruding third eyelids
Of all these symptoms, dilated pupils that do not respond to light are usually the first clinical sign. It is essential that you take your cat to the vet immediately to improve prognosis. There is no curative medication, and only a small number of cats ever make a full recovery.
Does your cat only have one eye that is constantly dilated? If so, your cat has anisocoria, which is where one of its pupils is a different size than the other. This is not a disease but rather a symptom of many other diseases.
Conditions leading to anisocoria include corneal ulcers, glaucoma, head trauma, and exposure to chemicals and toxins. If trauma is the cause, the anisocoria will likely be temporary and not last longer than a few hours. However, a trip to the vet is a must if it lasts over 24 hours.
During your appointment, your vet will identify the underlying cause, and treatment will start to prevent further detrimental effects. Because of the varied reasons, the treatment for anisocoria depends on the underlying disease responsible.
7. Feline Spastic Pupil Syndrome
If your cat has anisocoria that appears to alternate between eyes, this is called feline spastic pupil syndrome. This is a symptom of the Feline Leukemia Virus (FeLV). Other clinical signs of this viral infection are:
- Difficulties breathing
- Loss of appetite and weight loss
- Pale gums due to anemia
- Lethargy and general weakness
- High temperature and fever
- Dull, poor-quality coat
Feline Leukemia is a severe condition that affects the immune system and is the leading cause of death in cats after trauma. There is no cure for the disease, but regular check-ups and examinations can help prevent the infection from reoccurring and prevent complications.
Thankfully, there is also a vaccine for FeLV kittens can have from 8 weeks of age. It is recommended for all cats that go outside and could come into contact with infected cats. If you haven’t already, I suggest vaccinating your cat to protect against this nasty and life-threatening infection.
8. Ocular Tumors
There is a possibility that your cat has big pupils because of an ocular tumor. Ocular tumors can press on the muscles or vessels in the eye, meaning they cannot constrict as usual.
These tumors also cause intense pain in the eye region. As already discussed, pain has a direct correlation with pupil dilation. Other symptoms include:
- Inflammation around the eye
- Cloudy eyes and discoloration
- A misshapen iris
- Discharge from the eyes
- Glaucoma, another cause of pupil dilation
Ocular tumors may or may not be cancerous, but it is vital to get the tumor removed as a precautionary measure. Besides, removing the growth early will also limit the spread around the body. Small lumps can be removed using a laser, but your cat’s eye may need to be removed entirely for larger tumors.
9. Iris Atrophy
Old cats with dilated pupils could suffer from iris atrophy, an age-related condition. As cats get older, the colored part surrounding their pupil known as the iris degenerates and starts to thin.
Aside from giving your cat’s eyes their beautiful color, the iris is also a muscle that helps the pupil to contract in response to bright light. As this muscle thins, it gets weaker, making it harder to constrict the pupil. Therefore, older cats often have big, round eyes all the time.
Age-related iris atrophy is not curable – once the muscle has deteriorated, there is no fixing it. However, iris atrophy is not anything to worry about. Dilated pupils in cats cause no pain and rarely result in any long-term vision problems. The only change you may notice in your cat is that they become more sensitive to bright light.
10. Medication Side Effects
Another reason why some cats have round pupils is a side effect of the medication they are on. Opioids such as buprenorphine and drugs to treat hypertension often cause pupil dilation. You will likely know if this is why your cat has big pupils as it will, occur after you administer their medication.
Usually, this is due to overdosage. I recommend that you speak to your vet and see if you need to reduce the dose. You may also be able to switch to another painkiller that does not have the same side effects. All cats are different, so getting the treatment spot on takes a little time.
That said, dilated pupils are not a bad side effect and will not cause any harm. If the drugs benefit the underlying condition, your vet will probably suggest leaving the treatment as it is. It is better for your cat to have dilated pupils than for them to be in intense pain.
Why Are My Cat’s Eyes Dilated Sometimes?
If your cat’s eyes are always dilated, a trip to the vet is needed.
It is nearly always an indication that something is wrong with your furry friend. Eyes are very delicate, and all underlying conditions must be treated before they deteriorate and damage your cat’s vision for good.
However, it is normal for pupils to change size and react to different conditions. This is not a sign of concern and instead shows healthy eye function, allowing your cat to have better vision in different light conditions, as well as a natural response when excited or scared.
Here is a look at these normal causes for pupil dilation in more detail.
1. Better Vision
You will notice that your cat’s pupils change size in response to light. In bright light, the pupils constrict to protect the back of the eye, but in the dark, the eyes dilate to let as much light in as possible.
If you are wondering, “Can cats see in the dark?” their night vision is not perfect. However, they can see much better in low light conditions, which is all thanks to their pupils dilating and letting as much light into their eyes as possible!
This excellent low-light-level vision is essential for successful hunting. Cats will do the majority of their hunting at dusk and dawn when the light levels are low. By having responsive pupils and letting large amounts of light in, cats can see and stalk their prey better.
2. Surprise or Fear
Cat’s eyes will also dilate when they are surprised or scared. This is because cats produce large amounts of the hormone adrenaline when they feel startled.
This hormone causes several physical changes in their body, including causing cats’ pupils to dilate. This physiological change lets more light into the eyes and improves their vision so they can properly assess the danger and deal with it most effectively.
If your cat’s pupils are big and round, it is best to leave your cat be. Scared cats are more likely to attack or lash out in fear. Leave them time to settle and realize they are still in a safe space and approach them when their eyes are not dilated and are back to normal size.
3. Hunting & Playing
Cats’ eyes also dilate when they are hunting or playing. This is because of the hormone adrenaline. When hunting in the wild, cats need to be alert, fearless and have lots of blood flow to muscles so that they can successfully catch their next meal, and they rely on adrenaline for this.
For domestic cats, their version of playing is hunting – playing with toy mice, chasing bits of string, or pouncing on their cat kicker toy are all similar motions to hunting real-life prey. Therefore, playing has the same effect on the body. Adrenaline pumps around their bodies as they play, making their pupils involuntarily dilate.
You can easily tell the difference between play and fear by observing the environment. If you are playing with your cat or have just given them a treat, then it is safe to assume that their pupils are wide and dilated because they are excited. However, if they are hiding under your couch during a thunderstorm, they are likely scared.
MY FINAL THOUGHTS
Having pupils that dilate and constrict in different circumstances is a sign of good feline health. Yet if your cat’s eyes are always dilated it can be concerning. Cats’ eyes often give away a lot about how your cat is feeling and can be the first obvious symptom for many underlying conditions.
If you notice your cat has large pupils all the time, take them to the vet as soon as possible. Usually, hypertension is what is causing their pupils to dilate, which is a secondary condition for several illnesses. Therefore, it is important your vet diagnoses the underlying problem and provides effective treatment.
Other conditions could also be the culprit, and the majority can be managed with the correct treatment. The most important thing to remember is not to panic. Follow the advice of your vet and your cat will likely be well and back to good health in no time.
Hello! I have a 2-year-old Persian Punch Face Cat and his name is Casper, Casper was brought in last night and has been shaved due to the Vet’s recommendations. He is extremely scared and aggressive. Please help
Let's go Brandon says
I would like to add one that you sort of covered under medication and that is toxicity. I’ve seen this happen to some of the street cats here and I’m not exactly sure but I suspect it has to do with the pesticide that’s been sprayed on the foliage. We had five Street cats die within a week of them spraying the foliage last year. Cats are always chewing on grass so I think that’s how they got it into their system and I noticed that the ones that were getting sick and dying had this problem of constantly dilated pupil and it was sort of shiny looking glowing even in the daytime. Unfortunately I was not able to get them to the animal Doctor and they all died in the short time. We still have a lot more Street cats around here but I hate it when they die and sad for me to have to go and bury them in the back of the property line