It is normal 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 be an indication 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 become dilated when light conditions change, or to express fear, anxiety, or excitement. But when a cat’s eyes are constantly dilated it is a cause of concern.
Here are the most common explanations as to 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 right away if you notice anything funny with their eyes. It isn’t worth running the risk of leaving a potential medical condition unchecked.
High blood pressure, also called hypertension, is the most common reason why your cat’s eyes are always dilated. Cats with hypertension have blood pressure greater than 160mm Hg. Other symptoms of this condition aside from dilated eyes include:
- Excessive thirst and increased water consumption
- Bleeding from the nose and blood in the urine
- Muscle tremors and seizures
- An irregular heartbeat
Feline hypertension can be related to several factors, including kidney disease, thyroid problem, or heart disease, so be sure to take your cat to the vet so that they can prescribe effective treatment. The condition is also more common in older cats or those that are overweight or obese.
Unfortunately, it can be difficult for vets to diagnose hypertension. In fact, abnormalities in cats’ vision are usually the giveaway sign, such as your cat having large pupils that do not constrict bright light. 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.
The treatment prescribed by your vet will vary depending on the cause of feline hypertension. It is often a secondary result of other underlying conditions, with the most common causes being kidney failure or hyperthyroidism. It is also possible that there could be no obvious cause, but this is extremely rare in cats.
Even once on medication to reduce their blood pressure, cats’ pupils can remain dilated. This is because one of the drugs used to treat the condition can cause pupil dilation as a side effect. As long as you keep going to the vets to regularly check that their medication is still working, this is nothing to worry about. Cats with hypertension that are on the correct treatment can live long, happy, and fulfilling lives.
2. Blindness or Loss of Vision
If your cat is losing their vision, its eyes may also constantly be dilated. Just like how pupils dilate to aid our vision, cats that are struggling to see will have large pupils in an attempt to let as much light into their eyes as possible to aid their vision. This is their body’s way of trying to compensate for their deteriorating sense of sight.
Aside from cats having round pupils, signs of blindness or poor vision also include:
- Bumping into objects and acting clumsy
- Being overly cautious when jumping or climbing
- Acting more startled than normal
- Confusion and disorientation
Cats’ eyes do deteriorate with age. As such, if your senior cat has dilated pupils and is acting a little clumsy, blindness is a real possibility. Unfortunately, there is little we can do to prevent age-associated blindness other than asking for veterinary advice at the first sign of any eye-related issues. However, cats can also develop temporary blindness as a result of kidney diseases, feline herpesvirus, or even severe eye infections.
Always take your cat to the vet if you suspect that they are blind. If it is only a temporary problem, your vet will prescribe medication to treat the underlying condition. Once this condition is treated, their sense of vision should return. 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 is as simple as possible.
Thankfully, cats rely on their sense of smell, hearing, and touch to navigate through their environment a lot more than they do their vision. You may have to rearrange your living space to make it easier for your cat to navigate, but they will soon adjust to having poor or no vision.
3. Anxiety Disorder
Another reason why some cats have round pupils is anxiety disorder. Now, it is normal for cats’ eyes to dilate in response to fear. This is because when scared, the hormone adrenaline pumps around the body and triggers a “fight or flight” response. Adrenaline works on multiple areas of the body, including the pupils. The hormone makes them dilate to improve vision, giving cats the best chance of escaping the danger.
You may notice this reaction if there is a sudden loud noise that startles your cat or the presence of an unknown person or animal. Your cat will likely be alert with its eyes wide, ready to either fight or run from the imminent threat. However, if your cat’s eyes are constantly dilated because of fear, they 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 of neglect earlier on in life
- Long-term stressors in their environment, such as another pet they are constantly having to compete with
Sustained periods of high stress can trigger several other problems, including aggression or a loss of appetite. Therefore, it is important you try to understand the reason your cat is permanently stressed.
Start by assessing whether there have been any changes to their usual environment or routine. Has there been a change to their feeding schedule? Have there been new people or animals in your home? Are they having to compete for resources with other cats? If so, these changes are likely what has triggered this reaction in your furry friend.
You can try to ease your cat into the new environment to help them feel more comfortable. Also, make sure you add plenty of places for your cat to hide in your home, such as a cat caddy or cardboard boxes. This provides somewhere for your cat to retreat to if they become stressed and need some time out. If you live in a multi-cat household, make sure you have double of all the essentials, such as food and water bowls, litter trays, and cat beds as well.
On the other hand, some cats are naturally nervous by nature. In these cases, medication may help to calm them down and relax. Speak to your vet if you can’t seem to calm your cat down by improving their environment. If the treatment is working, you will notice your cat’s pupils contract.
4. Chronic Pain
As cat’s pupils dilate when they are in pain. Therefore, the reason why your cat’s pupils are so big constantly could be down to chronic pain. In fact, cats will instinctively try to hide that they are in pain because in the wild this will make them appear as a target to predators. Constantly dilated pupils are one of the only giveaways for cats who are in physical pain.
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. Here are a few of the most common pain-causing conditions your cat might be diagnosed with:
- Arthritis: With senior cats, a common problem is arthritis which can cause even more intense pain when moving. Aside from dilated pupils, you might notice your cat is more sensitive to touch, has stiff movements, and doesn’t jump or climb as it used to. Usually, painkillers and massage therapy can help ease feline arthritis.
- Dental Disease: Dental issues are another common issue, which is often accompanied by bad-smelling breath, difficulty eating, and inflamed gums. Plaque builds up over time, so these conditions are also more likely in senior felines.
- Soft Tissue Injury: There is a chance that your cat has sustained a soft tissue injury. This could have occurred from blunt trauma, overexertion, or repetitive strain. You’ll likely notice bruising under the skin, limping and stiffness, and swelling at the site of injury.
5. Feline Dysautonomia
Although extremely rare, your cat may be suffering from feline dysautonomia (also referred to a Key-Gaskell Syndrome). Unlike many other conditions on this list, it typically affects young cats.
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, among others. The ANS basically controls every essential bodily function that your cat needs to survive that does not require conscious thought.
For example, you don’t tell your heart to beat, it just does it. You don’t tell your stomach to break down your food, it just does it. You cannot tell your pupils to dilate or constrict, this just happens automatically. It is the same for your cat and most other animals. Cats with Key-Gaskell syndrome are unable to regulate these functions, and 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 is usually the first clinical sign that owners notice. It is important you take your cat to the vet immediately and document all the symptoms and when they started. This means your cat can get treatment before its condition deteriorates.
Unfortunately, it is not known what causes this condition. As such, only medication to treat the symptoms can be provided and most cats with this disease do not survive. For those that do, it can take up to a year to recover fully, and many will be left with some permanent dysfunction. Remember that this condition is extremely rare, though worth highlighting.
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 in itself, but rather a symptom of many other diseases.
Conditions that can lead to anisocoria include corneal ulcers, glaucoma, head trauma, and exposure to chemicals and toxins. Because of this, the treatment for anisocoria depends on the underlying disease that is causing it.
If your cat has glaucoma or a corneal ulcer, anisocoria may be accompanied by squinting or rapid blinking. Cats with glaucoma will also have bulging and bloodshot eyes too, along with behavioral traits due to the intense pain. Your vet may recommend surgery to remove the eye or ongoing drug therapy. Medication for pain relief is also commonly prescribed.
On the other hand, if your cat’s anisocoria is due to toxicity, you will notice several other warning signs. Examples of clinical signs include vomiting or diarrhea, tremors, muscle weakness, lethargy, and a reduced appetite. If trauma is the cause, the anisocoria will likely be temporary and not last longer than a few hours.
Regardless of what is causing anisocoria, a trip to the vet is a must if it lasts over 24 hours. The underlying cause will be identified, and treatment will start to prevent further detrimental effects.
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 serious condition that affects the immune system and is the leading cause of death in cats after trauma. However, cats can encounter the virus and fight it off, with 70% able to do this on their own. That being said, persistently infected felines will likely die within three years.
Because of this, if you notice your cat has feline spastic pupil syndrome then take them to the vet immediately. 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 a vaccine for FeLV that kittens can have from the age of 8 weeks. It is recommended for all cats that go outside and could come into contact with infected cats. If you haven’t already, I suggest getting your cat vaccinated to protect against this nasty and life-threatening infection.
8. Ocular Tumors
There is a possibility that cats whose eyes can’t constrict have tumors behind their eyes. The 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
Moreover, most tumors that develop within the eyes are malignant. This means they grow uncontrollably and can easily spread to other regions of the body. Therefore, the symptoms of ocular tumors are often much more widespread than you’d imagine and can cause pain throughout the body.
Ocular tumors may or may not be cancerous, but it is important to get the tumor removed as a precautionary measure. Due to the might malignancy of ocular tumors, removing the growth early will also limit the spread around the body. Thankfully, small tumors can be removed by using a laser. However, in the worst-case scenarios, your cat’s eye may need to be removed.
If this is the case, I would try not to worry. Cats adapt quickly and will have a perfectly happy life once they have become accustomed to having only one eye. As I mentioned earlier, they rely much more strongly on their sense of smell and hearing to navigate through their environment.
9. Iris Atrophy
Old cats with dilated pupils could suffer from iris atrophy as this is 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 a permanently dilated look.
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.
Because pupil dilation can be a symptom of a much more serious condition, such as hypertension, glaucoma, or blindness, it is still important to take your cat to the vet. These three conditions are all more prevalent in older felines, so it’s always worth checking they’re not dealing with one of these instead.
10. Medication Side Effects
Another reason why some cats have round pupils is a side effect of the medication they are on. Painkillers such as opioids are one of the most common types of drugs that cause pupil dilation in cats, such as buprenorphine. Drugs used to treat hypertension also have pupil dilation as a side effect.
You will likely know if this is the reason why your cat has dilated eyes because it will occur after each time you administer their medication. In addition, they may also suffer from other side effects of the medication such as excessive licking or pacing.
Usually, this is due to overdosage. I recommend you speak to your vet and see if you need to reduce the amount of medication you are giving your cat. You may also be able to switch to another pain killer that does not have the same side effects. All cats are different, so it can take a little playing around with different medications and dosages to get it spot on.
With that being said, dilated pupils are not a bad side effect and will not cause any harm. If the drugs are beneficial to the underlying condition, your vet will probably suggest leaving the treatment as it is. It is better for your cat to have dilated pupils all the time than it is for them to be in intense pain.
Why Are My Cat’s Eyes Sometimes Dilated?
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 ASAP 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 all of these normal causes for pupil dilation in more detail.
1. Better Vision
You will notice that your cat’s pupils dilate and constrict in response to changes in light levels. In bright light, they will constrict to protect the back of the eye, but in the dark, they will dilate to let as much light in as possible.
If you are wondering “can cats see in the dark?” their vision is not perfect, and they cannot see any more than we can in the pitch black. 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. This isn’t a necessity for domestic cats, but great hunting skills are imperative for the survival of wild cats.
Because of how your cat’s pupils respond to light, your vet will often use a bright light to test their eye function. If they shine a bright torch into your cat’s dilated eye and it does not constrict, they know there is an underlying problem.
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 startles. Large amounts of adrenaline running through their body triggers the “fight or flight” response and give them the best chance of survival.
How does this one hormone do this? Well, adrenaline makes cats feel fearless so that they are brave enough to tackle any dangers that come their way. But it also has physical changes on their body, such as increasing their heart rate. This quickened heart rate sends more blood to their muscles, heart, and lungs. Doing so primes them to run away from a bad situation or get ready to fight.
Another side effect of adrenaline is that it makes cats’ pupils dilate. This 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. It could be anything from a loud noise to an unknown house visitor that makes your cat feel scared. And 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 back to normal.
If cats’ eyes dilate when they are scared, then why do cats’ eyes dilate when they play? Are they scared of their toys? This often confuses owners but having dilated pupils can also be a sign of excitement. This seems confusing as two very opposite emotions trigger the same response in their eyes.
The reason cats’ eyes dilate when they play is that adrenaline is again pumping around their bodies. When hunting prey in the wild, cats need to be alert, fearless, and have lots of blood going to their muscles so that they can respond quickly and 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 as hunting. Adrenaline will be pumping around their bodies as they play, making their pupils involuntarily dilate.
You can easily tell the difference between excitement 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.
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 permanently large pupils, 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 at all.