What is Unequal Pupil Size?
Normally, the pupils expand and contract in unison. When unequal pupils occur, the abnormal eye can be either be 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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Symptoms of Unequal Pupil Size in Cats
Only one symptom need be present to merit a veterinary examination. If any of the following arise , veterinary attention is advised
- 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
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. Causes include:
- Concussion (bleeding and swelling of the brain from head trauma)
- Injury to optic nerves
- Neurological disorders (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)
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 carried out 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. Specific 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 suspected. 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.
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, reducing the intra ocular pressure and 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 side effects and treatment time 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 as needed.
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.
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
domestic cat
Two Years
21 found this helpful
21 found this helpful
My pet has the following symptoms:
One Eye Dilated Thr Other Not
I just came home from work and noticed. One of my cats eyes looked funny. Hr not acting his self. One eye is very very dilated. The other looks normal.
Feb. 10, 2021
Answered by Dr. Maureen M. DVM
21 Recommendations
Hello, sorry about that.
That sounds like a condition known as Anisocoria. It can occur as a result of many things such as corneal injury, neurological or brain injury, retinal disease among others.
It should be treated as an emergency. I would advise you to seek help from your veterinarian as if not attended to, it may result in vision loss.
Good luck
Feb. 10, 2021
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Unknown
One Year
70 found this helpful
70 found this helpful
My pet has the following symptoms:
One Pupil Is Small While The Other Is Large
She isn’t acting any different. Still eating, drinking, sleeping, and playing like normal. Just a few minutes ago I noticed one pupil was small while the other was big. This had to of just happened as it wasn’t like that an hour ago.
July 23, 2020
Answered by Dr. Michele K. DVM
70 Recommendations
Thank you for your question.
While a change in pupil size is definitely abnormal, if she is acting normal otherwise, it may be fine to keep an eye on her. If the problem continues over the next 12 to 24 hours, it would be best to have her seen by a Veterinarian, as they can assess her neurologic status. If things return to normal, it may have been a short-term problem, and it would be an okay to monitor her for any change in function. I hope that things go well for her.
July 23, 2020
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Domestic long hair cat
Seven years
11 found this helpful
11 found this helpful
My pet has the following symptoms:
Pupils Dilated To Different Sizes
My cat is acting slightly more agitated than normal and his pupils are different sizes. It has been quite hot the past few days, that might be behind in irritation. Should I bring him to my vet asap?
July 21, 2020
Answered by Dr. Michele K. DVM
11 Recommendations
Thank you for your question.
Heat does not cause a change in pupil size, and there may be something going on with your cats brain or neurologic system that needs attention. It would be best to have him seen by your veterinarian as soon as possible, yes. They will be able to assess his eyes and neurologic function, and see what might be the cause of the problem. I hope that all goes well for him.
July 21, 2020
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Tabby Cat
Obie
3 Years
2 found this helpful
2 found this helpful
My pet has the following symptoms:
Uneven Pupils
Puffy Tail Constantly
Overly Dilated Pup
Appetite Changes
I took my cat in a month ago to have his vaccines done and now his pupils are either really dilated or they are different sizes and his tail becomes puffy all the time there is something wrong with him
Sept. 8, 2018
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Short Haired Mackarel Tabby
Mr Dave
9 Years
10 found this helpful
10 found this helpful
My pet has the following symptoms:
Uneven Pupils
My cats eyes have odd pupils.
One is sometimes slightly larger that the other, they both react normally to light and such, contracting/dilating as normal. He has no other symptoms, and completely normal for him. Eating fine. Just the slightly different pupil sizes sometimes.
Sept. 3, 2018
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Main Coon
Milo
12 Years
0 found this helpful
0 found this helpful
My pet has the following symptoms:
Not Eating
Depressed
Dilated Pupil
Brief history of my cat: 12 years old; Siamese/Main Coon mix; long, thin build; very vocal and affectionate in his older age; mainly indoor cat with some outside time every day; will occasionally hunt/kill/eat birds/mice/rats/bunnies while outside; minimal vaccines and exclusively raw diet fed.
Milo came home one day with one dilated pupil. He wasn't acting weird or didn't seem in pain/discomfort other than one pupil was much larger than the other and he didn't open the affected eye all the way, just kinda half closed at times. It was so dilated that I could barely see any blue in his eye! He walked fine (jumping on furniture too), ate fine (whined for his dinner as usual), acted completely normal including purring loudly and whining to be let outside every morning. He had no injuries that we could find.
I took him to the vet the next day to get checked out and everything was normal- she couldn't find anything out of the abnormal, aside from his eye, so I decided on the "wait and see" method to see if things improved/worsened. At this point we had stopped letting him outside so we could keep an eye on him and prevent any possible injuries.
About 5 days after the discovery he wasn't acting normal any longer. Milo stopped purring loudly, he walked much slower and preferred to sleep all day. He also stopped "meowing" completely... our very vocal cat completely ceased being vocal. He even stopped whining to be let out every morning, which we stopped doing after the discovery of his dilated pupil. At this point I was starting to get worried. He seemed depressed.
A few more days passed and he stopped eating. He didn't stop completely but he ate so very little and for a thin cat, I was worried. I tried feeding him several different things and most of the time he would just take a nibble and be done. He was anxious to try everything I was feeding him but never really wanted it. It was about this time I noticed he wasn't sleeping as much.. still not purring or meowing but not as sleepy.
A week later he escaped the house and returned hours later. And to our astonishment, his eye returned to normal! Over the following days we noticed he was acting normal again (purring loudly, whining for his food and to be let outside). Three weeks after the discovery of his dilated pupil and he now seems completely back to normal, including eating his regular raw diet.
Russian blu mix
Talullah Belle
11 Years
0 found this helpful
0 found this helpful
My pet has the following symptoms:
Dilated Pupil And Siezures
I’ve witnessed my 11 year old cat have seizures, now one of her pupils is dialated and she seems afraid and is hiding under the dresser. Are these related symptoms or is this a separate thing?
Unequal Pupil Size Average Cost
From 370 quotes ranging from $200 - $4,000
Average Cost
$1,000
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