old cat with dilated pupils
Questions About Cats

Why Are My Cat’s Eyes Dilated All the Time? (Cat Pupil Dilation Meaning)

Cats dilate their pupils to improve vision. Wide eyes allow a cat to absorb more light, which is helpful in dim lighting. Pupils also dilate when a cat is excited, afraid, or hurt. This should never last longer than a couple of hours. Prolonged pupil dilation requires further investigation.

Constant dilation of the eyes is often linked to pain, overstimulation, or age-related atrophy. Your cat could also be sick. Multiple health concerns are connected to dilated pupils. The most serious of these are feline leukemia, toxicity, dysautonomia or tumors.

Cat’s eyes will always dilate periodically. It only becomes a concern if the pupils never contract. In these instances, your cat’s eyesight is eventually at risk. Diagnosing the issue is key to maintaining good eye health in cats.

Why Do Cat’s Eyes Dilate?

A cat most commonly widens its eyes to see clearer in dim conditions. Light enters a cat’s eye through the pupils. The more light a cat absorbs, the better it can see. A cat may seem to have constantly dilated pupils at night.

According to Brain Research, cat pupils expand up to ten times wider than those of humans. Dilated pupils in a cat are known as mydriasis.

If lighting is not dim, a cat will widen its pupils for a different reason. The most common explanations are:

  • The cat is shocked or startled
  • The cat is excited (often after spotting potential prey for hunting)
  • The cat is in pain
  • The cat is unwell
  • The cat experienced eye trauma

If the dilation is temporary, it is not a concern. Your cat could be in pain because somebody stepped on its tail. Apologize, let the cat sulk for a few minutes, and all will be fine. Likewise, a cat will soon recover from being startled by a loud noise.

If the mydriasis lasts more than a few hours, there will be a reason. This could be medical or psychological in nature.

My Cat’s Eyes are Constantly Dilated

A cat with constantly dilated eyes is a source of concern. Cat eyes should remain in a neutral state for the majority of a day. Dilation should be an exception, not the rule.

Cat eyes could remain dilated throughout a day and night for medical or psychological reasons. Common explanations for this issue include:

  • Blindness
  • Generalized anxiety disorder
  • Overstimulation
  • Chronic or constant pain
  • Consumption of toxins
  • Hypertension (high blood pressure)
  • Dysautonomia (aka Key-Gaskell Syndrome or Feline Dilated Pupil Syndrome)
  • Side effects of medication
  • Age-related atrophy of the iris
  • Ocular tumors

If your cat’s eyes are constantly dilated, something is wrong. Assess the cat’s behavior and attempt to find out the reason.

Loss of Sight

If a cat is losing its sight, eyes will remain dilated constantly. The cat is attempting to absorb as much light as possible to aid vision.

Senior cats often start to lose sight, especially purebred cats. The blindness could be temporary or permanent.

Aside from constantly dilated pupils, signs that a cat is going blind include:

  • Clumsiness and bumping into unfamiliar objects
  • Walking with whiskers low to the ground
  • Apprehension when jumping and climbing
  • Easily startled by sudden noises
  • Difficulty locating a water source
  • Excessive vocalization, growing distressed when you do not respond

You can test your cat’s eyesight with this simple method:

cats eyes always dilated

Wave a ball of wool before the cat. Don’t swing the wool close enough for the cat’s whiskers to feel it. If your cat can see, it will find the wool irresistible. Hunting instincts will kick in. A blind cat will remain indifferent.

If your cat has lost its sight, see the problem may be temporary. Kidney issues, toxicity, feline herpesvirus, and eye infections can all cause short term blindness. Your cat will require immediate treatment.

If your cat is permanently losing its sight, it will be fine in the longer term. Eyesight is widely considered to be a cat’s lowest priority sense. Cats rely more on hearing, smell, and touch. Just make some lifestyle adjustments:

  • Do not rearrange furniture
  • Provide obstacle-free paths to food, water, and litter
  • Stamp your feet when entering a room to announce your presence
  • Speak to your cat regularly as your voice will offer comfort
  • Avoid loud, sudden noises

You’ll soon find that your cat barely notices its lack of vision.

Tension and Anxiety

When a cat is frightened, its eyes remain wide and dilated. This means a cat with anxiety will have constantly dilated pupils. This must be managed carefully. Cats cannot comfortably live in a permanent state of anxiety.

If you notice wide-eyed fear in your cat, check for a trigger. This could be a loud noise or the presence of a stranger. Cats will also frequently flee and hide when startled. When the cat re-emerges, the eyes should no longer be dilated.

A cat that roams with dilated eyes seems continuously on edge. The cat fears danger at every turn. Eventually, this will take a toll. Health problems invariably follow prolonged periods of stress and anxiety. The cat can also become aggressive. Many cats consider attack is the best form of defense.

Learn why the cat is stressed and take action if applicable. Most often, cats are stressed because something in their routine has changed. Maintain a strict, reliable routine to keep your cat happy.

Some cats are nervous by nature. In these instances, utilize medication, calming scents and sounds, and herbal remedies. If the cat’s pupils contract, the calming techniques have been successful.


If a cat is not nervous, it could be overstimulated. Cats grow excited by sights, sounds, and smells. If the cat does not calm down, it will grow over-excited. That can place a strain on the heart.

Overstimulation is common when a cat finds itself in a new environment. The cat will grow excitable while exploring new surroundings. If you notice a new cat has constantly dilated eyes, guide it to a single room.

Once the cat has the chance to calm down, its pupils will follow suit. This will make the cat happier in the long term. It will eventually emerge from the room and continue exploration without concern.

Chronic Pain

Cats are adept at hiding physical pain. They are keen to avoid demonstrating discomfort. A cat that cannot walk without limping, for example, may not walk at all. It could be misconstrued as a sign of weakness.

Cats cannot hide all the symptoms of pain. Constantly dilated cat eyes are a giveaway. If your cat’s eyes are wide, look out for other symptoms of discomfort. These include:

Make your cat comfortable and attempt to decipher the problem. In senior cats, arthritis is an ever-present risk. This can be managed through massage and supplements. Painkillers will also be available upon prescription.

Pay attention to your cat’s mouth, too. If the cat has foul breath, it may be experiencing dental pain. Almost every cat will experience problems with its teeth eventually. Dental issues can be linked to further health complications. Have your cat’s teeth assessed.

cats eyes don't constrict

Toxicity and Poisoning

A cat that has consumed toxins will frequently display dilated eyes. The cat’s body is under attack. This will invariably lead to a range of side effects. In addition, your cat will be in pain.

Other than dilated eyes, warning symptoms of toxicity in cats include:

  • Vomiting and diarrhea
  • Trouble breathing
  • Weakness and lethargy
  • Muscle tremors
  • Low body temperature
  • Lethargy
  • Reduced appetite

Toxicity is a constant risk. If you can find no other reason to explain dilated eyes, consider this risk. Many house and garden items are toxic to your cat.

If your cat has consumed toxins, these must be flushed from your cat’s body. Never attempt to induce vomiting at home without advice.


Hypertension means that your cat has high blood pressure. If a cat’s blood pressure is 160/80 mmHg, it has hypertension. Older cats are particularly prone to this concern. The pain and discomfort associated with the condition lead to dilated eyes.

Hypertension in cats is often a secondary disease. It will often be linked to another, primary concern. This could be kidney or heart problems, the presence of a tumor, or diabetes. This means that hypertension should never be ignored. Aside from dilated eyes, symptoms include:

  • Excessive water consumption
  • Blood in the urine
  • Circling
  • Bleeding from the nose
  • Irregular heartbeat
  • Muscle tremors
  • Seizures

A cat that takes medication for hypertension will see a reduction in symptoms. Unfortunately, the cat may still have dilated eyes.

According to the Archives of Pharmacology explains, mydriasis is a side effect of Clonidine. This drug is used to treat hypertension.

Keep in touch with your vet and have your cat regularly tested. If the underlying cause of hypertension is treated, Clonidine will no longer be required. This will resolve your cat’s mydriasis.


Dysautonomia is a serious concern in cats. It’s also known as Key-Gaskell Syndrome, or the more on-the-nose Feline Dilated Pupil Syndrome. Dysautonomia attacks a cat’s automatic nervous system, or ANS. This means a cat has no control over basic functions.

As an aggressive and degenerative condition, dysautonomia must be treated urgently. Constantly dilated eyes are the easiest symptom to recognize. Other concerns include:

  • Digestive issues
  • Dry nose
  • Lack of appetite and associated weight loss
  • Regurgitation of food
  • Protrusion of the eyelid
  • Slow heart rate
  • Low body temperature
  • Inability to urinate or defecate

The Journal of Feline Medicine and Surgery describes an enlarged esophagus and swollen abdomen as the commonest warning signs. Be mindful of a wide-eyed cat that vomits or regurgitates food.

There is no cure for dysautonomia, but the condition can be managed. Thankfully, dysautonomia in cats is also rare. It typically manifests in young cats. A senior cat with mydriasis is unlikely to live with dysautonomia.

Iris Atrophy

As a cat grows older, its entire body starts to struggle. The eyes are no exception. The iris of a cat’s eye starts to thin. Once the iris degenerates, your cat will become unable to contract its pupils.

Iris atrophy is irreversible, but not serious. The cat will not be in any pain. It may become sensitive to bright light though.

The cat will squint and hide in dark corners. Provide an escape route from illuminated areas. This allows your cat the opportunity to rest its eyes.

Ocular Cancers and Tumors

When a cat develops a tumor behind the eye, it will often be malignant. This tumor can spread throughout the cat’s body. Urgent treatment is essential.

This will be painful for your cat, leading to dilated pupils. Other symptoms of a malignant tumor in a cat’s eye include:

  • Discoloration
  • Inflammation
  • Glaucoma
  • Discharge from the eye
  • Misshapen iris
  • Cloudy eyes

The diagnosis of eye tumors is completed using an ophthalmoscope. Biopsies will then be taken to determine the severity of the tumor.

If the tumor is small, it may be treatable by laser. In most cases, full removal of the eye will be recommended. This will prevent the tumor from spreading. Your cat will still live a full, happy life with one eye. The adaptation period will be short.

Only One of My Cat’s Eyes is Dilated

Mismatched pupil sizes in cats mean your cat has anisocoria. Sometimes, one pupil is smaller and permanently narrowed. It’s more common for one eye to be permanently dilated. Your cat may keep one eye closed.

Anisocoria is not a disease in and of itself. It is a symptom of another problem. Senior cats are prone to developing anisocoria. Common explanations include:

  • Physical trauma
  • Glaucoma
  • Ulcers on the cornea
  • Disease and infection within the eye
  • Feline spastic pupil syndrome

As with dual dilated eyes, anisocoria is concerning if it becomes a prolonged condition. Trauma, such as being poked in the eye, can cause temporary anisocoria. This should not last longer than a few hours.

If the anisocoria lasts over 24 hours, seek veterinary help. Tests will need to be run to diagnose the issue.

What do dilated cats eyes mean?

Eye Diseases, Ulcers, And Infections

Cats can be prone to a range of eye infections and diseases. These could be bacterial contagions, or due to irritation or allergies.

A basic eye infection will be treated with antibacterial eye drops. If successful, your cat’s eyes will return to an equal size.

Senior cats often develop ulcers on the eye. These will be removed using a scalpel. Ulcers are painful, but simple to treat. A vet will remove an ulcer on an in-patient basis.

A problem like glaucoma is more concerning. Glaucoma places pressure on your cat’s optic nerves. Left untreated, this could cost your cat her sight.

Feline Spastic Pupil Syndrome

This condition causes anisocoria to move from one eye to another. Feline spastic pupil syndrome is usually a symptom of feline leukemia (FeLV). If cat’s mismatched eyes vary regularly, it almost certainly has FeLV. This is a serious concern.

Feline leukemia is a highly contagious condition. It is passed on through blood, saliva or waste. If recurrent, the condition is lethal. FeLV is a vaccine offered to all kittens and adult cats. Additional symptoms of FeLV include:

  • High fever
  • Trouble breathing
  • Loss of appetite and weight loss
  • Pale and discolored gums
  • Sterility
  • Lethargy
  • Poor quality coat

There is no cure for FeLV. This is why vaccination is critical. If your cat is diagnosed with FeLV, keep it indoors. If the cat is infected once, it could catch the virus again. Mixing with other cats will always enhance this risk.

Cats have very expressive eyes. You will often see a cat with dilated eyes when it’s very excited, but a cat’s eyes shouldn’t be dilated constantly.