Eye care

Cat Third Eyelid Showing - Causes and Treatment

Josie F. Turner
By Josie F. Turner, Journalist specialized in Animal Welfare. Updated: October 22, 2023
Cat Third Eyelid Showing - Causes and Treatment

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The reasons a cat's third eyelid is showing can be benign, but it can also be a symptom of a serious disease. These can be bacterial infections or other diseases which affect the eye directly, but they can also be more systemic. Also known as the nictitating membrane, the third eyelid can appear in one eye or both, depending on the nature of the problem. Other concurrent symptoms can help us to determine the cause of the third eyelid showing. It is also possible for a cat third eyelid showing with no other symptoms. If you are at all unsure, you will need to take the cat to a veterinarian for diagnosis.

At AnimalWised, we look at the causes and treatment of cat third eyelid showing. We stress that it is important this problem is not ignored, especially if we observe other symptoms which indicate a local or systemic illness.

You may also be interested in: How To Clean Dog’s Eyes
  1. What is the third eyelid in cats?
  2. Causes of third eyelid showing in cats
  3. Cat third eyelid showing in one eye
  4. Cat third eyelid showing with no other symptoms
  5. Treatment for a third eyelid showing in cats

What is the third eyelid in cats?

The third eyelid is the common name for the nictitating membrane (palpebra tertia). It is a tissue located around the cornea, conjunctiva and mucous membrane. It is a translucent or semi-transparent additional eyelid found in various animals, including the cat.

Although you may not notice, you can often see secretions between the eye and the outer eyelids when your cat is half asleep. As they wake up, a cat's third eyelid showing as they begin to open their eyes is normal. However, it should not be visible once open, awake and alert.

The purpose of the third eyelid in cats is not completely understood, but we do know it serves important functions. They include the following:

  • Protection: one role of the third eyelid is to protect the eyeballs from any foreign object and from traumas such as when a cat is fighting or playing. The appearance of a third eyelid is instinctive and automatic. It is also responsible for releasing a liquid with antiseptic properties to fight bacteria and microorganisms that could cause disease. However, these protective uses of the third eyelid should not lead to the feline nictitating membrane to show all the time.

  • Moisturizing: nictitating membranes are also sometimes known as a 'haw'. In other animals, including many birds, it can be used to moisten the eyeball while open. As it is transparent or translucent, it means the animal can still see. Some mammals have a full third eyelid which can do this, but the cat does not. It is believed that some species have evolved away from using this membrane. Even humans have a vestigial part of their conjunctiva known as the plica semilunaris which is thought to have once been a third eyelid.

If you see that your cat's third eyelid is visible, either in one eyeball or in both, this means that they are in pain or suffering from a condition or disease[1]. Some research suggests that the appearance of this membrane is related to intestinal feline parasites and digestive problems, whereas others state that if this membrane is visible then the problem is related to the eye itself.

In these latter cases, the problem with the cat's inner eyelid could be due to a prolapse[2]. In order for you to have all the information, we will show you the causes that can cause this tissue to appear in your cat's eye.

Causes of third eyelid showing in cats

If you see that your cat's nictitating membrane is visible in one or both eyes, it is usually a symptom of a secondary problem. These are some of the root causes of a cat's third eyelid showing:

  • Conjunctivitis: this ocular infection doesn't only cause the appearance of the third eyelid, but is also causes swelling, tearing and lacrimation (tearing).

  • Dehydration: when the cat is suffering from a severe lack of water, the appearance of this ocular tissue is a sign and symptom of a serious health condition. They will need to be treated by a specialist who will need to replace fluids and treat the underlying cause of dehydration if necessary.

  • Wounds: if your cat has suffered a blow or trauma to the face, both of its eyes may have become affected. Infection is also possible. Take them to the vet straight away to treat infection and repair any damage.

  • Foreign body: anything that gets into the cat's eyes, whether plant matter, dust or anything else, will cause the nictitating membrane to appear, as it is a mechanism to prevent it from further embedding into the eyeball.

  • Cancer: it's possible for this small organ to be affected by the formation of cancer cells in cats. Fortunately, the disease is relatively rare in this part of the eye. Unfortunately, if it does occur, then it can progress quickly and become fatal[3].

  • Haw's syndrome: this name is given to the appearance of the third eyelid when related to an intestinal problem from which the cat is suffering or has suffered from recently. Examples include intense diarrhea in the cat or the presence of parasites. With Haw's syndrome in cats, the third eyelid turns into a protrusion thanks to prolapse. It most commonly occurs in cats less than 2 years of age. Prolapse of the nictitating membrane is one of the most common issues with third eyelids in dogs[4].

  • Parasites: an infestation can be one of the causes of haw's syndrome, but the parasites itself are the problem. Different types of cat worms can lodge themselves in the eye, potentially resulting in blindness if not treated promptly.

  • Genetics: some cat breeds, such as the Burmese cat, might be prone to suffering a rupture or protrusion of this membrane inside the eye, which is very uncomfortable for them.

  • Dermoid cyst: a dermoid cyst is one which is present at birth and can grow slowly as they age. It is usually not observed until secondary symptoms occur. One case study on a kitten with third eye showing from 2016 shows that it can be present on any part of the eye. The result is still protrusion of the nictitating membrane[5]. However, the same study notes that any ocular dermoid occurs infrequently and can respond well to treatment.

The length of time the third eyelid is showing will correlate to the cause. As we said, it may appear for moments after sleeping. However, even once the cat begins treatment, the nictitating membrane may still be visible. This is because the cat's body is taking time to heal.

Furthermore, if you see the third eyelid in your cat it is also highly likely that its eyes will start to tear. They will probably try to touch them with their paws owing to the discomfort caused when this membrane is out of place. So if we see our cat scratching at their face or rubbing it too frequently, we should look to see if we can observe the third eyelid showing.

Cat Third Eyelid Showing - Causes and Treatment - Causes of third eyelid showing in cats

Cat third eyelid showing in one eye

As a note, if a cat's inner eyelid is showing in one eye and not the other, it is still a cause for concern. It may imply a problem on one side of the body, but it still means there is an issue which needs resolving. It might be that you see a cat's third eyelid showing in one eye which progresses to both. This implies the progression of one of the causes listed above.

If a cat third eyelid showing in one eye is observed, it could be some direct damage to this membrane. This would explain why it is visible in one eye and not the other. It could be a piece of dust which has lodged within or even something hitting it. As we have stated above, cancer is a possible cause of protrusion in the third eyelid, but this is relatively rare. Regardless if a cat's nictitating membrane is observed in one eye or two, you should take them to the vet for evaluation.

Cat third eyelid showing with no other symptoms

If we see a cat's third eyelid appearing due to one of the above reasons, we are likely to see other concurrent symptoms. This could be the presence of a wound on their body or even itching in the case of parasites. However, it is also possible that the cat's third eyelid shows without any other symptoms. This can complicate diagnosis. While it does not always indicate an immediate health emergency, several potential reasons for third eyelids showing without other symptoms:

  • Mild Irritation: subtle eye irritation can be caused by minor allergies, dust or exposure to irritants in the environment. These mild irritations can cause the nictitating membrane to become visible temporarily. In these cases, it may resolve on its own as the irritant is cleared from the eye.

  • Physical exertion: cats may sometimes exhibit their third eyelid during strenuous physical activity or play. This is generally a temporary response and is not concerning if it occurs during energetic play or exercise.

  • Sudden bright light: a cat's pupil adjusts to different lighting conditions. Abrupt exposure to very bright light can cause the nictitating membrane to appear. This is a normal reaction and should subside once the cat adapts to the lighting.

  • Sleep or relaxation: cats in a very relaxed state or transitioning between sleep and wakefulness may briefly display their third eyelid. As the cat becomes more alert, it should retract.

  • Constitutional anatomy: some cats may naturally have a more visible nictitating membrane due to their individual anatomy. This is usually not a cause for concern as long as the cat's eyes are otherwise healthy.

  • Temporary discomfort: the cat may be experiencing mild discomfort that hasn't yet manifested in other symptoms. This could include minor eye irritation, an initial stage of an eye condition or early signs of a systemic issue.

While the visibility of the third eyelid alone may not be an immediate cause for alarm, it is essential to monitor your cat for any changes in behavior, appetite or additional symptoms. If the third eyelid remains visible or if you notice any other concerning signs, you should consult a veterinarian.

Cat Third Eyelid Showing - Causes and Treatment - Cat third eyelid showing with no other symptoms

Treatment for a third eyelid showing in cats

Owing to the various reasons that can cause the cat's nictitating membrane to occupy more space in the eye than it should, there are several types of treatment. This treatment depends on the source of the problem.

  • Dehydration: if a lack of water causes your cat's third eyelid to show, you should give the cat plenty of wet food and water in order to halt the process. It is also recommended to take the cat to the vet if the animal has been lacking water for an extended period of time. They may need additional help such as fluid therapy.

  • Disease: some of the common diseases in cats result in the cat's third eyelid to appear. Treatment will depend on the underlying cause. Bacterial infections such as those that cause conjunctivitis will require antibiotic treatment, often in the form of antibiotic eye drops such as Tobrex for cats. Systemic illness may require more invasive treatment such as surgery and/or chemotherapy for cancer. The nictitating membrane should retract after successful treatment.

  • Foreign body: since the third eyelid helps to lubricate the eye for this very purpose, the foreign object may remove itself naturally. If it doesn't, the eye will need to be flushed out. If removal is difficult, it may be best to take the feline to a vet.

  • Haw's syndrome: the third eyelid should disappear by itself, once the intestinal and digestive problems that caused the appearance of the membrane go away. In turn, this will lead to the nictitating membrane gradually disappearing as the cat returns to health.

  • Genetic condition: when a genetic reason is behind cat third eyelid showing, the vet will use various diagnostic tests to determine whether the cat's inner eyelid membrane is affecting the cat's vision and causing discomfort. If this is the case the vet may also resort to surgery. This process will not to extract their third eyelid, but will put the feline nictitating membrane back into its correct position.

If you are unsure of why a cat's third eyelid is appearing, you will need to take them to a veterinarian for assessment. They can confirm the underlying cause and administer the correct corresponding treatment. Learn about another potential eye health problem with our article on corneal ulcer in cat eyes.

If you want to read similar articles to Cat Third Eyelid Showing - Causes and Treatment, we recommend you visit our Eye care category.


1. Muir, P., et al. (1990). A Clinical and Microbiological Study of Cats with Protruding Nictitating Membranes and Diarrhoa. Vet Rec, 127(13), 324-330.

2. Williams, D., & Middleton, S. (2011). Everted Third Eyelid Cartilege in a Cat: A Case Report and Literature Review. Veterinary Ophthalmology, 15(2), 123-127.

3. Komáromy, A. M., et al. (1997). Primary Adenocarcinoma of the Gland of the Nictitating Membrane in a Cat. Journal of the American Animal Hospital Association, 33, 333-336.

4. Edlemann, M. L., et al. (2013). Investigating the Inheritance of Prolapsed Nictitating Membrane Glands in a Large Canine Pedigree, Veterinary Ophthalmology, 16(6), 416-422.

5. LoPinto, J. A. (2016). Dorsoally Located Corneal Dermoid in a Cat. JFMS Open Rep, 2(1).

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What did you think of this article?
Very informative, better than other articles I've read about this. Appreciated.
Great comments too. Feel reassured that I know what to do/look for.
Administrador AnimalWised
We're glad we could be of help!
Very informative - much appreciated
Administrador AnimalWised
We are glad we could be of help, Gail!
My kitten is about 5 months old, hasn't gotten their first vaccine yet due to low number of vaccines my local vets has.
His third eye is only showing in one eye, and usually closes it. He eats and drinks alright, but just worried and not sure when to bring to vets; was thinking of lightly dapping their eye with warm water on cotton wool. Not sure what else I could do?
Take it to a vet that does have medicine. What kind of vet doesn't have vaccines ? A cat showing that isn't really a problem my cats do that all the time. Its if there is a change of color in that . Then there is a problem. A cat that is sleepy might show that while waking up or going to sleep. If it shows all the time, go to a vet, if it changes color, go to a vet. If you cant hasn't been vaccinated ..... GO TO A VET !
What would happen if the nictate membrane is not treated? Would it heal by itself or not? Our cat suffered a trauma to the head and we have no vet nearby.
Administrador AnimalWised
Hi Keanna,

In most cases, the visibility of the 3rd eyelid means there is a systemic problem. Rarely does it mean there is only a problem with the eye. However, as the article states, there are many reasons why this may be. Only a vet can diagnose it. Not only do they have the knowledge, but they have the right diagnostic tools to discern the problem.
Debbie Roberts
Fantastic information for my animal care course - thanks :-)
Hello I have a kitten he is over 8 weeks old so he is a good size but I’ve been feeding him puppy food ( a starter formula ) because he likes it and I’m not sure if he is food poisoned but his third his lid is showing , he eats and he drinks water but he sleeps all day plz help what can I do ( also I’ve started feeding him cat food now since his eyes did that .
Do not feed it puppy food
Amos tjuku
My cat has a nictating membrane that is not regrating yet it is well fed.Offer. possible treatment options for conjuvictis in cats
Administrador AnimalWised
Hi Amos,

This could be due to a wide variety of reasons, as stipulated in the article. We know it is difficult to see vets at the present moment, but you should still be able to call your local vet and relay the symptoms. They will be able to advise on the best course of action and let you know what options there are.
I read that the common cause is a URI (Upper Respiratory Infection). Proved true for my cat...
nancy hudgins
is it possible, that right after birth the claws from the kitten itself injured the eye? I mean I know that she did stick her claw into her eye, I was trying to feed her the bottle and she was grabbing and poked her eye I actually had to remove her hand from her face the claw was in her eyeball. I never realized kittens claws stayed out like they are always visible until that happened I feel so horrible and have zero income and her mother passed that's why I was having to bottle feed in the first place, but she now is two months old and her little eye is smaller than other one and just looks so uncomfortable to her I feel like it is all my fault cause of ignorance and letting her flap her hands around and trying to grab her bottle, but she is big girl now and drinking her milk from a bowl and eating big girl food as well but I am heart broken over her eye I will try post pic .. nm cant upload pic from phone to pc sorry but it is only the one eye that is affected with the third eyelid showing and that is the one she poked as newborn
Administrador AnimalWised
Hi Nancy,

It is possible, it would also likely cause an obvious injury to eye and may even bleed due to trauma from the claw. We cannot confirm either way, but a third eyelid showing can be a sign of illness, something a vulnerable kitten needs addressed immediately, so we recommend going to the veterinarian just to be sure.
Richard O. Green
Can I help my 6 month old kitten naturally, third eyelid has shown since eyes opened, they are very red and she's always having nose and eye discharge. On fixed income and can't afford a veterinarian. Trying chamomile tea
Administrador AnimalWised
Hi Richard,

It is common for us to receive messages about people being unable to pay bills, but unfortunately there is no other option other than taking them to a professional. If you can't pay a veterinary bill, you should contact a local animal shelter or animal authority. They may be able to help or at least point you in the right direction. This kitten's symptoms sound very serious (especially if they haven't been vaccinated/dewormed). Their life may be in danger.
Hi! After a brief nap today with the kitties I suddenly noticed Zelda's left inner eyelid wasn't fully retracting. She was fine all day up until now. At first I just assumed she hadn't fully woken up yet, as I know that's normal to see the eyelid when they first wake up, but then she started rubbing her eye and I knew something was up.

She and her brother are very well hydrated. They drink their water and I feed them wet food twice a day, so I don't think hydration is the issue. If I had to guess, something must have gotten into her eye.

Do I need to take her to the vet or does this sort of situation resolve itself with time (like within 24 hours)? Thank you!
Administrador AnimalWised
Hi Alex,

It is possible there is something in her eye which has agitated the third eyelid. However, it is also possibly the beginning of an infection or some other issue. Unfortunately, we could not possibly diagnose this problem ourselves, nor can you. Only a qualified vet can do this. If it has not cleared up on its own and you see other symptoms appear, it is very important you take them to get checked. Good luck, we wish Zelda all the best!
I was laying next to my cat and she was sleeping then the third eyelid started showing but as soon as she woke up it was gone is this bad? or does it just happen when your cat is sleeping?
Administrador AnimalWised
Hi Romina,

This is a good question. When a cat is closing its eyes to sleep, you can often see the third eyelid, it is just a natural action. If it is not displayed when the cat is asleep, they should be fine. However, if you are in any doubt or they are showing other symptoms, you should take them to the vet. Hope this helps!
Michael marocco
My cat has the third eyelid showing my cat is vomiting, refusing to drink, not moving much we do not know what to do or what he has
Administrador AnimalWised
Hi Michael,

Neither do we as it could be a wide range of possible issues. What we do know is that your cat is showing signs of potentially serious illness. You need to take them to the vet immediately if this is the case.
This is my adorable, handsome lil man. I love this baby to the moon and back. He is my heart and my world. The world revolves around him in my eyes. He is very loveable and playful, eats like a pig and sleeps on my chest every night. Well, not long ago he developed some sort of eye infection in one eye and soon spread to the other eye. There was like a yellowish looking mucus coming from his eyes and his 3rd eyelid now covers like half his eye. They were also swollen bad and red. A friend recommended terramycin so that's what I purchased. I put it in his eyes 2-4 daily and now they are no longer swollen or red nor is there any mucus coming from his eyes but the 3rd eyelid is still covering half his eyes. Any suggestions on what to do next? Thanks in advance.
Administrador AnimalWised
Hi Sherry,

You should not treat eye infections like this on your own. It requires the diagnosis of a professional. If you are fortunate and the terramycin has worked, it is possible the infection is on its way out. However, the cat may need different types of antibiotics or the red eye is the symptom of a different disease. We cannot diagnose it here, so we recommend taking them to the vet to be sure.
Sherry have No idea if you will ever see this but perhaps someone that’s having similar problems will use this.
The primary cause of third eyelid showing through my experience with my own cat is a URI which is an upper respiratory infection. And that takes antibiotics ASAP. The longer that the infection is in their body then if we can use them for their old age diseases
Administrador AnimalWised
Hi Shirley,

Thank you for pointing this out. Since the nictitating membrane acts as a sort of ‘beacon’ for infections, almost any type can cause the eyelid to show. While we cannot find any report to conclude an URI is the most common cause of third eyelid showing in cats, it is an important one, so we have made this clearer in the article. Thanks again for sharing your experience!
My cat had a complete tooth extraction 2 months ago . She has been doing just fine until this last week. One side of her face has began to swell and her 3rd eye is showing. She still has a appetite but many times when she eats the food falls out of her mouth. Is there anything I can do to help her? What may be causing this?
Administrador AnimalWised
Hi JB,

You should take them to the vet. Inflammation implies infection, so they will likely need antibiotics. Whatever is the issue, they will need a vet to confirm the diagnosis.
Luke Goulden
Can anyone recommend a brand of drops that will help with this? We have 3 cats all of which have never had such symptoms but all are showing it all of a sudden. Thanks Luke
Melanie Newington
My cat had an eye infection and the 3rd eyelid was showing. I felt extremely concerned. After 2 courses of eye drops, improvement was still very slow. It has taken over 6 weeks to get back to normal, what a relief! Sometimes nature has to run its course.
Administrador AnimalWised
Hi Melanie,

We have many comments from people who have experienced the same situation. Unfortunately, convalescence isn't an instantaneous process, sometimes these things take time. As hard as it can be to have patience, it is a necessity sometimes.
Jason O
My cat ever since I got him as a kitten about (6 months old) from a local petsmart has always had this problem in one eye and has never shown any signs of discomfort, pain, or anything like that. Quite the Opposite actually he’s a playful happy healthy sweetheart but I’ve always wondered why his eyes like this. It really doesn’t seem like it could be anything on the above article because he has no symptoms of being sick or uncomfortable. The only reasonable explanation above is he had some sort of trauma before he was adopted by me. So I guess what I’m wondering is if that’s even the cause what kind of treatment can he get or what can I do for him?
Administrador AnimalWised
Hi Jason,

It is indeed possible that your cat has had some sort of trauma, but it is impossible for us to tell though these comments. It is also possible that the cat has a disease which is otherwise asymptomatic. This means there could be a problem, but you won't know it until the disease has progressed far enough. One such disease is chronic kidney failure. You should be taking your cat to the vet for regular checkups (once or twice a year). If they are due, you should take them along and find out just to be sure. They may need to run blood tests or other diagnostic tools.
Shannon J Rothberg
We have a few cats who have all developed some issue with their 3rd eyelid showing (where it had not been in the past). Our vet was no help. The cats (3 cats) otherwise seem fine. No parasites in the litter box. All indoor cats. One cat has loose stools (all her life - she is 2yrs old) Obviously the issue is due to something contagious. Any ideas? Thank you!
Administrador AnimalWised
Hi Shannon,

We cannot diagnose anything in these comments. We can maybe suggest something, but if your cat is unwell, you will need to see a vet. Particularly with a third eyelid showing, the causes are various and many conditions share symptoms. If you are unhappy with your vet's advice, you should get a second opinion and explain your situation. We're sorry if this isn't the answer you are looking for, but it would be irresponsible of us to provide another one.
Please help. My cat has had third eyelid showing for 5 days. Taken to vets and initially was due to bad allergies (which are cleared now) but the eyelids are still showing and seem to be getting worse. They are almost covering entire eye. We are giving him eyedrops (vet subscribed) but no impact. We have also been back to the vet twice (different vet 3rd time) and they have given him the all clear for other health conditions that could be causing it. Am I being impatient? Should the eyelids be back to normal by now?
Administrador AnimalWised
Hi Gen,

If your cat's third eyelid is showing, they will need a physical examination by a veterinary medical health professional. Since you have been to the vet 3 times and have had a second opinion, then this will imply you will need to wait for the symptoms to go down. However, this is only a suggestion, it is possible these vets have missed something, but we would think it unlikely. Keep an eye on related symptoms and if they seem to be getting worse in general then the only thing you can do is take them to the vet.
My cat had an eye infection and the 3rd eyelid was showing. After visiting 2 different vets and 2 lots of eye drops, improvement was really slow. I have been very concerned. After 6 weeks things are looking normal again. I think sometimes nature has to run its course and heal naturally.
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Cat Third Eyelid Showing - Causes and Treatment