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, and tumors.

A 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 eyes through the pupils. The more light, the better it can see. So, a cat may seem to have constantly dilated pupils at night.

According to Brain Research, cat pupils expand up to 10 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 that the cat is:

  • Shocked or startled
  • Excited, perhaps due to spotting prey for hunting
  • Pain
  • Unwell
  • Experiencing eye trauma

If the dilation is temporary, it is not a concern. Your cat could be in pain because somebody stepped on its tail. 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 that is 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 of the eyes should be an exception, not the rule.

A cat’s eyes could remain dilated throughout the day and night for medical or psychological reasons. Common explanations include:

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

Loss of Sight

If a cat is losing its sight, its 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’s eyes. Don’t swing the wool close enough for the cat’s whiskers to feel it. If your cat can see, its hunting instincts will kick in. A blind cat will remain indifferent.

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

If your cat is permanently losing its sight, it will learn to cope. Eyesight is widely considered to be a cat’s least effective sense. Cats rely more on hearing, smell, and touch. Just make some lifestyle adjustments:

  • Do not rearrange the 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 because your voice will offer comfort.
  • Avoid loud, sudden noises.

Tension and Anxiety

When a cat is frightened, its eyes will remain wide and dilated. A cat with anxiety will have constantly dilated pupils. Cats cannot comfortably live in a permanent state of anxiety.

If you notice wide-eyed fear in your cat, you’ll need to identify the trigger. This could range from a loud noise to the presence of a stranger. Cats will also frequently flee and hide when startled. When the cat re-emerges from its hiding place, its eyes should no longer be dilated.

A cat that roams with dilated eyes seems continuously on edge. The cat fears danger at every turn. Health problems can follow prolonged periods of stress and anxiety. The cat can also become aggressive.

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 and contented.

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 due to sights, sounds, and smells. If it does not calm down, it will grow over-excited, placing 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 had a chance to calm down, its pupils will follow suit.

Chronic Pain

Cats are adept at hiding physical pain. A cat that cannot walk without limping, for example, may not walk at all.

Cats cannot hide all the symptoms of pain, and constantly dilated cats’ 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.

If the cat has foul breath, it may be experiencing dental pain. Most cats will eventually experience problems with their teeth, and dental issues can be linked to further health complications.

cats eyes don't constrict

Toxicity and Poisoning

A cat that has consumed toxins will frequently have dilated eyes. Aside from eye dilation, warning symptoms of toxicity include:

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

Toxicity is a risk because so many home/yard items are toxic to cats. If your cat has consumed toxins, these must be flushed from the body.


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

Hypertension is often a secondary disease. It can be linked to another, health concern, such as kidney or heart problems 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 experience a reduction in symptoms. Unfortunately, the cat may still have dilated eyes. According to the Archives of Pharmacology, mydriasis is a side effect of Clonidine. This drug is used to treat hypertension in cats.


Dysautonomia, also known as Key-Gaskell Syndrome or Feline Dilated Pupil Syndrome, attacks a cat’s automatic nervous system (ANS). This means a cat has no control over its 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.

Iris Atrophy

As a cat grows older, its iris starts to thin. Once the iris degenerates, your cat will become unable to contract its pupils.

Iris atrophy is irreversible, but the cat will not be in pain. It may become sensitive to bright light, though. The cat will squint and hide in dark corners, so provide an escape route from illuminated areas.

Ocular Cancers and Tumors

When a cat develops a tumor behind its eye, it will often be malignant. This tumor can spread throughout a cat’s body. This will be painful for your cat, leading to dilated pupils. Other symptoms 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 needed to prevent the tumor from spreading.

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 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, though. If the anisocoria lasts over 24 hours, your cat should be checked by a vet.

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, or due to irritation or allergies.

A basic eye infection can 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 can be treated. 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 its 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 a cat’s mismatched eyes vary regularly, it almost certainly has FeLV.

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 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, which 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 increase this risk.

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