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Home > Cats > Why Is My Cat’s Third Eyelid Showing? Vet Approved Facts & FAQ

Why Is My Cat’s Third Eyelid Showing? Vet Approved Facts & FAQ

owner holding cat with third eyelid visible

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Dr. Lauren Demos

Veterinarian, DVM

The information is current and up-to-date in accordance with the latest veterinarian research.

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When you’re a cat lover, you love everything about cats, and there’s no question that a cat’s eyes are one of the most beautiful things about them! But have you ever noticed your cat’s third eyelid and wondered why it’s showing?

Several issues can cause the third eyelid to show. Some are serious, like conjunctivitis, and others are easily treated, like removing a foreign object.

Here, we explain the third eyelid, how it helps cats, and the different conditions that can affect it.


What Exactly Is the Third Eyelid?

The third eyelid, or the nictitating membrane, can be found not only in cats but also in many other species as well. It adds an extra layer of protection. For example, it helps protect a camel’s eyes against blowing sand and enables a frog to see underwater.

Cats have the standard two eyelids that we all do: the lower and upper eyelids that we use for blinking or closing when sleeping. The third eyelid is found in the inner corner of the eyes. It’s a membrane that covers the eyes when the cat sleeps and retracts when they’re awake.

There are tear glands known as a lacrimal gland in the corner of the eye that produce tear film to moisten and lubricate the eye and help remove and protect the eye from debris.

Most of the time, we can’t see the cat’s third eyelid except when they are waking up. You might notice it sliding back into place when your cat starts to open their eyes. But it isn’t normal to see your cat’s third eyelid when your cat is awake and alert, which is usually a sign that something is wrong.

orange tabby domestic shorthair cat with haw's syndrome where the third eyelid is covering part of the eye
Image Credit: Mary Swift, Shutterstock


What Are the Causes of the Third Eyelid Showing in Cats?

If your cat’s third eyelid is showing in one or both eyes, there’s typically an underlying issue. The following are common causes of a visible nictitating membrane.

1. Conjunctivitis

Conjunctivitis is inflammation of the tissues around the eye. It can be quite painful and generally requires treatment.

Other signs include:

  • Inflamed and swollen tissues around the eye
  • Discharge from the eye that can be clear or colored
  • Cat squinting and unable to open or close the eye completely
  • Pawing at the face and eye

If it has been caused by an upper respiratory infection, you might also notice the following signs:

  • Nasal discharge
  • Sneezing
  • Lack of energy
  • Loss of appetite
adult cat with herpesvirus infection and purulent conjunctivitis
Image Credit: Todorean-Gabriel, Shutterstock

2. Injury

An injury or wound to the cat’s eye can lead to the third eyelid showing. Other signs that your cat might have an injured eye are:

  • Visible foreign object in the eye
  • Clouded cornea
  • Protruding eye
  • Blood in the eye
  • Squinting
  • Distorted pupil (shaped differently or abnormal reactions)

3. Haw’s Syndrome

Haw’s syndrome occurs when the nictitating membranes are seen suddenly in both eyes. Sometimes this is accompanied by gastrointestinal issues, though not always. It’s rarely known what the cause is, but it’s thought that things such as parasites or viruses that cause inflammation in the gastrointestinal tract may contribute.

Other signs include:
  • Lethargy
  • Diarrhea
  • Lack of appetite
shorthair cat with a severe case of Haw's syndrome, where the third eyelids or nictating membranes are covering both eyes
Image Credit: Mary Swift, Shutterstock

4. Foreign Object

The nictitating membrane was designed to prevent and remove foreign bodies from the cat’s eyes. If a foreign object isn’t removed by the membrane, it could lead to irritation and inflammation and the third eyelid remaining over part of the eye.

5. Corneal Ulcers

Corneal ulcers are caused by damage to the cornea, which is the transparent membrane found at the front of the eye. This condition is painful.

Other signs of a corneal ulcer include:
  • Squinting the eye
  • Redness of the eye
  • Rubbing the eye with a paw or against other surfaces
  • Eye discharge
kitten with conjunctivitis and corneal ulcer
Image Credit: Todorean-Gabriel, Shutterstock

6. Uveitis

The uvea is a part of the eye (it includes the choroid, ciliary body, and the iris), and uveitis is inflammation of the uvea.

Signs of uveitis are:

7. Horner’s Syndrome

Horner’s syndrome occurs when there’s damage to the nerves connected to the affected eye and the facial muscles. It can be caused by a tumor or trauma, but sometimes the cause is unknown. The vet can treat the underlying cause, but often Horner’s syndrome resolves itself.

Other signs can include:
  • One pupil being more constricted than the other
  • Noticeable third eyelid on the eye with the constricted pupil
  • Sinking of the eye into the head
  • Drooping upper eyelid on the affected eye



When Is It Okay to See Your Cat’s Third Eyelid?

When your cat is relaxed and sleepy, seeing some of the nictitating membrane is quite normal. You’re also likely to see it when your cat wakes up gradually.

If your cat sometimes sleeps with their eyes partially open, you will often see the membrane, and again, this is nothing to worry about. But as soon as your cat is completely awake and alert, you shouldn’t be able to see it.

Additionally, if your cat is sedated or put under anesthesia, you’ll see the third eyelid when they are coming out of it. It might last a few hours, which is also normal, but if it remains on your cat’s eye the next day, see your vet.

How Is a Visible Third Eyelid Treated?

There isn’t any one way to treat a visible nictitating membrane. It has multiple causes, so how it’s treated depends on what is causing it. Your vet will run tests to determine the cause and treat it accordingly.

cat eye checkup
Image Credit: santypan, Shutterstock

Can You Treat a Visible Third Eyelid Yourself?

Absolutely not! As you can imagine, the eyes are quite delicate, and it doesn’t take much to damage them.

Even if your cat seems perfectly fine with some of their third eyelid showing, you should still call your veterinarian. They can offer advice for the next steps, which might include a visit to the clinic.



If you’re not sure if you’ve ever seen your cat’s third eyelid, just watch when they slowly wake up, and you might catch it sliding back into place. But there are a multitude of reasons that the nictitating membrane will stay in place even when your cat is awake.

If this is the case for your pet, you should always get in touch with your vet. Many of the causes are serious and painful for cats, and we want to keep them happy, healthy, and pain free for as long as possible.

Featured Image Credit: Me Gi, Shutterstock

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