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What is Unequal Pupil Size?

Normally, the pupils expand and contract in unison. When unequal pupils occur, the abnormal eye can be either the smaller (constricted) pupil or the larger (dilated) pupil. There may or may not be other symptoms present. If unequal pupils occur suddenly, bring your cat to a veterinary clinic or animal hospital immediately as eyesight can be permanently damaged if the problem is not rectified. Certain underlying causes of unequal pupils can be life threatening.

Unequal pupils, or anisocoria as it is called in the medical community, occurs when one of a cat’s pupils (the black openings in the center of the iris) is either too far open or too far closed in relation to the other pupil. This gives the appearance of a small black dot in the center of one eye and a larger black dot in the center of the other. This condition is often the result of a more serious complication within the cat.

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Unequal Pupil Size Average Cost

From 370 quotes ranging from $200 - $4,000

Average Cost

$1,000

Symptoms of Unequal Pupil Size in Cats

Only one symptom need be present to merit a veterinary examination. If any of the following arise after head trauma, veterinary attention will be needed immediately. 

  • One pupil larger than the other
  • Eye producing discharge
  • Drooping eyelid
  • Redness of the eye
  • Clouding cornea
  • Bluish cornea
  • Head tilting
  • Eye pain or irritation
  • Squinting
  • Activity decrease
  • Abnormal eye movement
  • Confusion
  • Change of position of eye in socket
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Causes of Unequal Pupil Size in Cats

Unequal pupils can be caused by both neurological (brain or nerves) and ocular (eye) issues. Because the eyes are so closely connected to the brain, often damage and injury of this area affect both parts of the body. All known causes include:

  • Concussion (bleeding and swelling of the brain from head trauma)
  • Injury to optic nerves
  • Neurological disorder (such as Horner’s Syndrome)
  • Oculomotor nerve paralysis (damage to the nerve controlling eye movement)
  • Cerebellum (brain) injury
  • High blood pressure
  • Corneal ulcer or injury
  • Glaucoma (pressure from excess fluid dilates the pupil)
  • Anterior uveitis (inflammation of urea constricts the pupil)
  • Retinal disease
  • Scar tissue
  • Iris atrophy (mainly in older cats)
  • Defective iris from birth
  • Cancer or cancerous tumors
  • Spastic pupil syndrome 
  • Feline leukemia virus
  • Stroke (ruptured blood vessels in the brain)
  • Eye infection
  • Medication (some can cause the pupils to dilate)
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Diagnosis of Unequal Pupil Size in Cats

To start the diagnostic process, the vet will require your cat's full medical history along with all current prescriptions ,including eye drops. Next, the vet will complete a physical examination with detailed focus on the eye region. You will be asked if your cat has undergone any recent trauma that you are aware of. The main objective will be to determine if the unequal pupils stem from a neurological problem or an eye problem. 

Many tests may be administered at this point. Often, the function of the pupils will be evaluated using Visual Pathway Testing. This includes checking for blinking reflexes, object following ability, and proper light sensitivity. Tear production may be measured with a Schirmer Test. Topometry may be applied to test for intraocular pressure. The cornea may be stained with dye to better find ulcers, scratches or other injuries. An ERG (electroretinography) test may be conducted to measure the function of cones and rods within the eye. 

Biopsies or conjunctival scrapings may be collected and sent to labs for further analysis. Blood tests and complete blood counts may be needed in cases which Feline Leukemia Virus or cancer are suspected. An ultrasound, MRI or CT scan may be requested if tumors or lesions are present. Spinal fluids may need to be collected and analyzed in some cases of neurological issues. Urinalysis may be needed in cases of infection. Obvious signs of disease will be noted for diagnostic purposes. If no cause is found, the cat may be referred to an ophthalmologist for further inspection.

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Treatment of Unequal Pupil Size in Cats

As unequal pupils are often the sign of an underlying issue, treatment depends on the issue and not the condition of the pupils themselves. Severity of underlying issues range from harmless to life-threatening. Common issues and their recommended treatments are listed below.

Medication 

In some cases, a medication will be found to cause unequal pupils. If this is the situation, the removal of the medication should stop the pupil issue. 

Glaucoma 

Often medication will be prescribed for this condition, fixing the unequal pupils in the process.

Infection 

If eye infections are found, the responsible bacteria will be identified and the appropriate antibiotics will be prescribed. The average time needed for antibiotics is 2-4 weeks.

Cancer 

If tumors are found, surgery may be an option. The cat would be put under general anesthesia for the procedure. Recovery time will depend on the location of the tumors. Radiation or chemotherapy may also be treatment options to fight against cancer. Both have strong side effects and treatment can be lengthy.

High Blood Pressure 

This can be alleviated with ACE (Angiotensin Converting Enzyme) inhibitors, beta-blockers, calcium channel blockers and a low sodium diet. This treatment may be ongoing. 

Horner’s Syndrome 

This issue will generally resolve on its own, but eye drops may be prescribed to help with symptoms. 

Feline Leukemia Virus 

No cure is currently known, so care designed to ensure the cat’s comfort would be advised.

Hypoplasia & Iris Atrophy 

Both of these conditions require no treatment. 

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Recovery of Unequal Pupil Size in Cats

Depending on the underlying cause of the unequal pupils, recovery can be possible. Often medications will be prescribed over a long period of time. If vision loss or blindness have occurred in the cat, they are often not reversible.

If Feline Leukemia Virus is found to be the cause, focus on all at home adjustments you can make to lengthen your cat's life span. This would include keeping the cat indoors, removing all sources of stress, changing the cat's vaccination schedule, following all antibiotic prescriptions for related infections closely and giving your cat vitamins and anti-viral drugs.

No matter what the underlying cause of unequal pupils is, if the condition does not improve, or if it gets worse, more veterinary care may be needed. 

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Unequal Pupil Size Average Cost

From 370 quotes ranging from $200 - $4,000

Average Cost

$1,000

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Unequal Pupil Size Questions and Advice from Veterinary Professionals

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Bailey

dog-breed-icon

Domestic shorthair

dog-age-icon

2 Years

pill-rating-filledpill-rating-filledpill-rating-filledpill-rating-filledpill-rating-filled

Fair severity

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4 found helpful

pill-rating-filledpill-rating-filledpill-rating-filledpill-rating-filledpill-rating-filled

Fair severity

Has Symptoms

Unequal Pupil Size

About a week ago I noticed my cat had one super large pupil and one very small pupil. She was acting completely normal (kept getting excited for a treat when I called her name to look at her and was running around) but I kept an eye on her pupils and they returned to normal after about 15-20 minutes. I didn't remember to look it up until four days later and saw this could be a sign of something super serious. It's been about a week now and since then her pupils have been normal and she seems to be acting normal as well. I keep looking for a cloudy eye or drooping eyelid and I think I'm just being paranoid but I want to be sure she's okay!

Aug. 31, 2018

Bailey's Owner

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Zoey

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Domestic shorthair

dog-age-icon

9 Years

pill-rating-filledpill-rating-filledpill-rating-filledpill-rating-filledpill-rating-filled

Mild severity

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0 found helpful

pill-rating-filledpill-rating-filledpill-rating-filledpill-rating-filledpill-rating-filled

Mild severity

Has Symptoms

Anisocoria

Our 9-ish year-old cat has had sporadic occurrences of anisocoria since she was a kitten. Typically her pupils go back to normal in a few days. Recently, however, she collapsed and could not stand for about 30 seconds, was lathargic afterwards, and we took her to an emergency vet. They found no infections or parasites, and suggested a neurological cause. Since then, she has had two or three incidents of anisocoria that resolved themselves in a few days as usual, and no repeat of the collapse. What is going on with my cat?

Aug. 24, 2018

Zoey's Owner

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0 Recommendations

It is difficult to say what is causing the anisocoria in Zoey, however in these chronic cases from kittenhood it is possible that no cause can be found. It would be best to consult with a Neurologist and possibly get an MRI too. Regards Dr Callum Turner DVM

Aug. 24, 2018

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Hopey

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Chartrueax

dog-age-icon

13 Years

pill-rating-filledpill-rating-filledpill-rating-filledpill-rating-filledpill-rating-filled

Mild severity

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0 found helpful

pill-rating-filledpill-rating-filledpill-rating-filledpill-rating-filledpill-rating-filled

Mild severity

Has Symptoms

Uneven Pupils

I think she has recently had a stroke or suffered a leg injury, so she had a limp for a while but it progressively got better. She’s been walking normal for about a week now ( the “injury” causing the limp only lasted about 2 weeks max) and now she has uneven pupils. It seems as if she got a cut in her eye, she wants to try to keep it closed for longer periods of time but when it’s open it’s completely dilated. Not sure if it’s more of a sign for a stroke or maybe she just hurt herself.

Aug. 19, 2018

Hopey's Owner

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0 Recommendations

There are a few different causes for anisocoria (unequal pupil size) including head trauma, stroke, tumour, eye injuries, glaucoma, other ocular conditions among other causes; I cannot say whether the change in pupil size is due to an injury to the eye (scratch) or something more serious, you should visit your Veterinarian for an examination to be on the safe side. Regards Dr Callum Turner DVM

Aug. 19, 2018

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Rhiannon

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Domestic Longhair Cat

dog-age-icon

13 Years

pill-rating-filledpill-rating-filledpill-rating-filledpill-rating-filledpill-rating-filled

Mild severity

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0 found helpful

pill-rating-filledpill-rating-filledpill-rating-filledpill-rating-filledpill-rating-filled

Mild severity

Has Symptoms

Eye Is Smaller Than The Other One

Hi, my 13 year old kitty had 6 teeth removed 4 days ago. And we noticed the next day that one of her eyes were a little bigger then the other one and the pupil seemed larger in one eye. Called the doctor the next day and he said if it doesn’t improve over the next day or two to bring her back. Well here it is Sat night and we noticed that her eye is still larger then the other one. I’m starting to freak out. I can’t bring her to the vet until Monday. Is this normal after having surgery? She is acting totally fine but she keeps squinting a little on the one eye. Any thoughts would be great please I’m freaking out.

July 22, 2018

Rhiannon's Owner

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Dr. Michele K. DVM

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0 Recommendations

Different sized pupils can be a result of pain, nerve trauma, or brain disease. With Rhiannon, if it happened after the dental, it may be a result of nerve trauma to the nerves of her eyes, and it may be a temporary thing. If she is generally doing well otherwise, isn't having any balance problems, is eating well and not painful or pawing at that eye, having her seen on Monday should be fine.

July 22, 2018

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Tootsy

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long hair

dog-age-icon

1 Year

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Fair severity

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pill-rating-filledpill-rating-filledpill-rating-filledpill-rating-filledpill-rating-filled

Fair severity

Has Symptoms

Eye Discharge
Dialated Pupil

My kitty tootsy whom I’ve had since birth was fine and was just chasing a fly when she comes back to see me her pupils are different sizes and I got very scared (one is normal size and one is “skinnier”). Everything else is fine and I don’t know what it could be? She did have a little bit of eye discharge 2 days before the dialated pupil episode. She is also pregnant maybe high blood pressure? Otherwise she is healthy eating fine and being her jumpy self. Should I worry?

July 13, 2018

Tootsy's Owner

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0 Recommendations

Anisocoria may be caused by a number of different conditions which may include trauma (to the head or eye), eye disorders (glaucoma, uveitis etc…), poisoning, neurological disorders among other conditions; you should keep an eye on Tootsy for the time being and visit your Veterinarian for an examination to be on the safe side if there is no improvement or you suspect she may have injured herself. Regards Dr Callum Turner DVM

July 14, 2018

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Jinx

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Tortoiseshell

dog-age-icon

3 Years

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Fair severity

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0 found helpful

pill-rating-filledpill-rating-filledpill-rating-filledpill-rating-filledpill-rating-filled

Fair severity

Has Symptoms

Pain
Lump
Discomfort
Abscess
Uneven Pupils

She goes out a few times a day, normally never far or long. Went out one evening for less than a hour. Comes back and her backend, right above her tail bone was super sensitive to the touch. Thought maybe she fell, mom even mention maybe a male cat thought she wasn't fix and took advantage of her. It didn't seem to bother her, she was walking around fine, eating/drinking, using her box like normal. The next night I notice a lump. Next day, I shaved her back end, I barely touched the lump and the abscess started to express itself. Does seem like she may have been stung or bitten by something. I've trained as veterinarian technician and this isn't my first abscess. After the abscess was expressed and cleaned, I had to put a made wrap on it until I could get a cone. Now looking her over, I noticed one of her pupils is smaller. I don't know if this is connected to the bite or the stress of me having to shave her and express her. We have a vet appointment Friday.

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Gracie Reylen Dockery

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stray

dog-age-icon

1 Year

pill-rating-filledpill-rating-filledpill-rating-filledpill-rating-filledpill-rating-filled

Fair severity

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0 found helpful

pill-rating-filledpill-rating-filledpill-rating-filledpill-rating-filledpill-rating-filled

Fair severity

Has Symptoms

Runny Nose
Swollen Puffy Around Left Eye
Runny Goopy Eye
Normal Right Pupil And Constricted

My husband and I were living with a friend who had several cats well when we moved Gracie came with us...weve been at our new house maybe a month and this morning when I came out to feed our cats we have 2 Gracie and amm but only Gracie came from our friends Gracie was laying on our porch rail with a swollen eye it was goopy and running her nose was running and her left pupil was constricted her eye is not swollen shut but she is squinting she still seems to be able to see but I'm concerned for her her abnormal pupil will barely dilate at all it is only a small slit I'm worried that the goopy runny eye and the runny nose may signal an upper respiratory infection but I'm not sure...because of her unknown history I'm not sure what all she has been through or if she has ever had any previous problems...we are pretty sure she is descended from our other cat amm since amm lived at our old house before I met my husband and then she came to live here with us...i do not know her age or if she has ever been pregnant before...im thinking she may be pregnant now...once when I was holding her she was drooling just a bit but I was told several years ago when a cat I had back then drooled really bad that it's because he was weened to early bringing her inside isn't a good option because she sprays...on everything (maybe the move to a whole new place stressed her out I have no clue) she is the sweetest cat...im worried about her but I'm also concerned that whatever she has may be contagious...my grandmother had two cats but only one is left and every now and again her eye will swell shut (her eye lid is what swells you can't even open her eye because the bottem eyelid is so swollen her eye does leak but her pupils are normal and this happens over and over again my grandma puts a medical cream in her eye and she gets better almost overnight it seems so I do not think my Gracie has whatever is wrong with hers I just want my Gracie to be ok (oh and both my grandmother's cats the girl and the her brother who is now gone had this eye problem they were my cat Amms babies but amm never had that problem) I just hope this is nothing deadly I lost my polydactal kitty bandit and Gracie helped cheer me up I love my Grace Grace

dog-name-icon

Thomas P. Cat (TOM)

dog-breed-icon

Siamese

dog-age-icon

19 Years

pill-rating-filledpill-rating-filledpill-rating-filledpill-rating-filledpill-rating-filled

Critical severity

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1 found helpful

pill-rating-filledpill-rating-filledpill-rating-filledpill-rating-filledpill-rating-filled

Critical severity

Has Symptoms

Skinny And Weak
Skinny And Weak Unequal Pupil

My Siamese is 19yrs. Old he lost a lot of weight so I took him to the vet and he was diagnosed with kidney disease/failure and thyroid disease they put him on methamazole 5mg 2x day he gained some weight but had emergency out of state with my wife and I was gone six weeks with her finally passing my neighbor took care of the cat but ran out of the meds for 3weeks I took him back to vet and they restarted the meds and he started to gain weight again for maybe a week but then stopped eating dry food and would only eat wet food again losing weight until just about a skeleton he also had an incident where he acted like he was having a seizure for about 5 seconds then he acted like he was drunk for a couple Of hours but got Better but not normal he also had one pupil larger than the other with some discharge so back to the vet for blood work and when it came back they increased his methamazole to 7.5mg 2x day and said his kidneys #s looked slightly better and his liver #s were off just a little checked blood pressure Wich was fine and an eye infection so antibiotic drops were prescribed it's been 10 days now and his eyes are better but still one pupil larger than the other and no weight gain still losing weight and he eats 3 to 5 cans of wet food a day and a couple of slices of turkey lunch meat and drinks slot he uses the box regularly but sometimes goes a day with no BM but always has one the following day I've been expecting him to die but he keeps hanging on is there something else that I might be missing or that I can do for him I've had him since he was weened and it's hard to watch him just turn into a skeleton with skin on it he doesn't act like he's in any pain and sits in my lap and purrs all the time if you have any thing to help I would be more than grateful Thank You

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Tarzan

dog-breed-icon

Cat

dog-age-icon

2 Years

pill-rating-filledpill-rating-filledpill-rating-filledpill-rating-filledpill-rating-filled

Moderate severity

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0 found helpful

pill-rating-filledpill-rating-filledpill-rating-filledpill-rating-filledpill-rating-filled

Moderate severity

Has Symptoms

Uneven Pupils

What if your cat, which is 2 and half years old, is experiencing the unequal pupil sizes, and had head trauma as a young kitten. It’s been over two years since then. I just don’t want him to be in pain, he seems okay but I wanna be certain.

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Flash

dog-breed-icon

stray

dog-age-icon

2 Years

pill-rating-filledpill-rating-filledpill-rating-filledpill-rating-filledpill-rating-filled

Moderate severity

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1 found helpful

pill-rating-filledpill-rating-filledpill-rating-filledpill-rating-filledpill-rating-filled

Moderate severity

Has Symptoms

Bump, Swollen Area, Eye Leakage

I think my cat might have been hit in the eye a few days ago. He had a bump on his head and wouldn't open his eye that much. The bump has gone away now but that pupil stays dilated. Any idea what's wrong?

Unequal Pupil Size Average Cost

From 370 quotes ranging from $200 - $4,000

Average Cost

$1,000

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