That Mysterious Third Eyelid

Jun 5, 2011 by Dr Diana Lafer    13 Comments    Posted under: Tips & Advice

For many owners, the appearance of their cat’s third eyelid is cause for great concern and confusion.  Never fear- it can often indicate a problem, but with a little information, you can better determine why this might be happening and how quickly your cat needs professional medical attention.

First, a bit of background:  The third eyelid provides an extra layer of eye protection for cats and many other animals.  Other names for the third eyelid include the nictitating membrane, nictitans and haw.  Arising from the corner of the eye nearest the nose, the retractable third eyelid can be hidden from view or can extend across the surface of the eye.  It is white to light pink in color and lies on top of the eye, but underneath the eyelids.  It contains cartilage and a tear-producing gland at its base.  When irritated, it can appear reddened.

While birds and reptiles can actively move this protective eyelid into position, in cats the movement is passive. It is kept hidden by forward pressure of the eyeball in the socket. When danger to the eye is anticipated ( such as in a cat fight), cats use a special muscle behind the eye to pull it back into the socket slightly, allowing the third eyelid to quickly move up and across the surface of the eye. If the eye does become injured and painful, cats will use this special muscle to pull back the eye slightly and allow the third eyelid to cover the eye as protection.

Damage to the nerve control of the third eyelid will also result in a prominent (or more visible) third eyelid.  Damage affecting one eye can occur due to an injury or inflammation after surgery (especially ear or dental surgery).

If you notice that one of your cat’s third eyelids is covering one eye more than the other, it is likely that your cat has injured that eye.  Eye injuries are painful and can become serious quickly, so you should seek veterinary care right away.

What does it mean if both third eyelids are visible?  There are a variety of reasons for this to occur.  First of all, when cats are in a deep sleep or have been given a sedative, the third eyelids can become prominent.  If your cat has lost a lot of weight, the fat pad behind the eyes may also have decreased in size, changing the position of the eye in the socket and allowing the third eyelid to become visible.  Rarely, inflammation due to a neurologic, respiratory or intestinal infection can affect the nerve control of the third eyelid.   Your cat should be examined by a veterinarian in order to determine a likely cause and how best to treat the condition.

If you have never seen your cat’s third eyelid, and want to know what to look for, ask your veterinary at your cat’s next check-up.

Dr Diana Lafer

Dr. Diana Lafer founded Cats Limited in 1995. She earned her bachelor’s degree in biology from Wesleyan University and her veterinary degree from Cornell University. Dr. Lafer has a cat (Sparky), and a dog (Lucy). She enjoys spending time with her daughters, horseback riding, skiing, hiking, participating in triathlons, and volunteering for the Lakeville Pony Club.

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  • Lisa R.

    My cat had a dental cleaning under anesthesia today and I was just about to call the emergency line until I read this post… thank u!  

  • Bandbkar

    thank you for this information.My husband and I rescued a kitten between 9 to 12 weeks.A group of kids was throwing rocks at this poor kitten, to make a long story short I think they damage his eye,and then there are other problems to he has a URI and his eye is leaking fluid, we are trying to get him stable enough to take him to a shelter to be adopted out. There at the shelter he will get more medical attention so in the mean time I wanted to get more info about his third eye lid. Thank you very much.

  • jlung

    Bandbkar, we’re glad we could help.

  • Lori_taylor001

    I rescued my cat about a week ago, but I’m worried about his vision. I only really noticed it yesterday, he can see – just not everything. Like he chases shadows on the ground but struggles to see a ball flying through the air. Also I’ve never seen his third eyelid, I did the menace test and he didn’t blink. I even managed to touch his eye and his third eyelid didn’t show ( I didn’t touch it on purpose, he moved) he can’t follow my finger in the air, but sees the shadow. He can move around fine, but struggles to jump from surfaces. Any thoughts?

  • http://www.facebook.com/people/Marcus-Brown-Dvm/100003861340496 Marcus Brown Dvm

    Lori,
    You need to get him to a veterinarian to assess his eyes.  There are many reasons why his vision may be compromised.  Some of these may be corrected if treatment starts early.  He most likely has third eyelids, but that too would be assessed during a physical examination. 
    Best wishes and good luck with your new guy.

    • Lori_taylor001

      Hey Marcus, thanks for replying. I took him to the vet and they say his eyes are fine that maybe he’s still getting used to his new home. He’s been treated for parasites and ill be going back in a few weeks for his vaccines. I’ll have them check his eyes again, to make sure. Structurally they’re fine though, which is a relief. Thanks again

  • Sandra Jackson

    How much of visible third eyelid showing in cat, should be cause for concern. He follows things fine. I have a battle with fleas, he perfers outdoors. He his lean, very active hunting, I think he might be to thin. Do all these symptoms tie in together.

  • Magdalena Belza

    Hi if you could help me, my cat started showing in both eyes 3rd lids, and been to te vets who checked his eyes, and gave all clear that there is no damage, got the steroid eye drops, been applying those drops for over a day, and his eyes are still pretty much the same, how long do i have to wait and see if those drops should work? Thanks

  • chloe atkinson

    i have a 2 year old brain damaged cat which we rescued at 8 weeks old. for the last few days he had dissapeared and when he arrived home this morning i noticed that his 3rd eyelid was covering almost 1/2 of his eye and am very concerned due to his underlying condition and i cannot get him in at the vets for a few days, any advice would be much appreciated.

  • Karen

    My Bear Bear was diagnosed with hyperthyroidism, we have had a time of it but today I got the news his T4 is normal, however when I was at the vet this saturday for blood work, and also got his ears cleaned as we were using the ear gel for they hyperthyroid and now we are on pills; we returned home to find his third eyelid covering his Left eye. I brought him back to the vet who stated it was neurologica ideopathic in nature. I thought they may have got the ear cleaner in his eye. But he is also having moments lasting about 1/2 hr to 1hr, where he seems lethargic wobly in his back end, will not eat or drink, not himself. Could he be having TIAs or Seizure, how would I know the difference, could the medication be causing htis?

  • Meghan

    I am concerned that my almost 4-month-old kitten’s vision is being compromised. I’m worried that my step-father’s smoking habit might have anything to do with his left third eyelid’s showing. I wonder if I should take him to the vet. I’ve expressed my concern to my mother and hope to take him soon, seeing as its been showing and contracting for almost four days now. My mom and I have been putting medicated eye drops we’ve had for some time in his eye, and I’ve been doing my best to keep his eye clean using warm water on a clean paper towel. He and my other 1-year-old cat play frequently, but I watch them closely and they don’t seem to play too rough. However, the cheek under left eye has also deformed, and the pupil doesn’t seem to be any smaller or bigger than the right eye. I try my hardest to keep him away from the smoke as much as possible, but it doesn’t provide much comfort to me to know that he still smokes, aware of the damage it causes, and can cause. My 1-year-old had the same issues with his eye, but recovered on his own. Though I fear my 4-month-old is too weak to fight a possible illness on his own. Mind though, the third eyelid does retract when the eye is wiped. What does this mean? Does he have something in his eye? Or is his eye infected? Also, he paws at his eye and squints frequently. When he wakes up, unless his eye is cleaned it won’t open anymore than half way. Please suggest something for me to try to convince my mother to do. I am worried for my kitten’s health.

    • Meghan

      He also has a consistent diet of hard food sometimes topped with Special Kitty brand wet food, the same as our 1-year-old. The water he drinks is filtered regularly. He used to get bowls of store-bought milk every day, but that’s becoming rarer now since we can’t leave the milk in the bowl for more than a day. So now, he gets it every once in a while. Could that be anything, at all a contributing factor to his eye? I want to supply as much information as I can. I really care about this little dude.

      • http://www.catslimited.com Diana Lafer, DVM

        Meghan,

        I’m sorry to hear that your little guy is having eye trouble. You should definitely have your vet examine him. There are a variety of causes for the symptoms you are describing and it’s important to start treatment as early as possible. It is less likely to be caused by the second hand smoke, but there are other serious problems we worry about with cigarette smoke exposure (see this article: http://felinedocs.com/dr-diana-lafer/cats-and-cigarettes-a-lethal-combination/).

        Good luck with your kitten. I hope he is feeling better soon.

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