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How Many Eyelids Do Cats Have? Can We See Them All?

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By Nicole Cosgrove

white cat lying on log

Humans have two eyelids which we blink involuntarily to keep our eyeballs coated with moist basal tears. Cats have what’s called a nictating membrane, a third eyelid. Unlike the other two eyelids, which move vertically across the eye, the nictating membrane moves horizontally.

Usually, the third eyelid stays tucked out of sight in the central portion of the eye socket, near the nose. It’s a moist membrane that can sometimes have a distinct coloration from the eye, usually dark-colored or very pale, occasionally pink from the blood vessels running through it.

The third eyelid swipes horizontally across the eye, much like windshield wipers, to keep the eyeball moist and protect it from debris and harm as the cat moves about. Traditionally, this protection would be most useful as the cat moves through underbrush while hunting.

Should I Be Able to See My Cat’s Third Eyelid?

As we’ve covered, the third eyelid is usually tucked into the central corner of the eye socket and move back and forth over the eye in a horizontal blinking motion. However, there are times and conditions where you might see the nictating membrane peeking out into the open. Some are harmless and normal, but some indicate a further illness that pet parents want to address.

tabby cat eyes
Image Credit: MelaniMarfeld, Pixabay

Born That Way

Some cats are born with a more prominent third eyelid or a smaller eye socket which causes the nictating membrane to appear protruded into the eye. If your cat has sort of always been that way and your vet hasn’t mentioned anything before, then it’s probably just the way your cat is shaped and is no cause for concern.

Some breeds, like the Siamese, are well-known for having more prominent third eyelids that may be visible even when the cat is awake and alert.

cat blue eyes
Image Credit: Andreas Lischka, Pixabay


One of the most common times to see your cat’s third eyelid is when they’re sleepy or asleep. Many cats sleep with their eyes partially open. This is normal and isn’t a cause for concern; some people even do it! When the cat’s eyes are “closed” yet remain “open,” the nictating membrane may become visible over the look, shielding it from damage. It’s normal to see your cat’s nictating membrane when they’re in a state of heavy relaxation, such as sleeping or during anesthesia.


Pain in the eye can cause the eyeball to retract into the socket and make the third eyelid appear to cover it. If your cat has developed a sudden protrusion of the third eyelid when they usually do not show much of the membrane, you’ll want to look for other signs of pain in the eye, such as rubbing or scratching at the eye and squinting. This will be the first thing to bring up to your vet when you take your cat in.

The most common causes of eye pain are inflammation of the eyes or respiratory system. This could be due to a foreign object, such as a dust particle or a spray of water, in the eye or any number of non-serious occurrences. However, if the protrusion persists, it’s essential to have your cat seen by a vet to rule out any serious complications with the eyes.

cat and vet
Image Credit: Stock-Asso, Shutterstock

Serious Foreign Obstruction

When we get some dust or water in our eyes, we rub our eyes with our hands to clear out the foreign objects, and your cat’s third eyelid does that job for them. However, larger foreign objects, foreign objects that have gotten stuck, or foreign obstructions in the eye can cause the third eyelid to be more prominent.


Conjunctivitis, or pink eye, is an inflammation and infection of the conjunctiva, the mucous membrane that lines the outer eyelids. To clear away the gunk produced by the conjunctiva, the nictating membrane may be more prominent or even stuck closed, much like a human’s eyelids but horizontally.

Conjunctivitis is a reasonably severe condition, even if it isn’t usually deadly. You should see your vet right away if you suspect your cat has conjunctivitis.

Vet dripping drops in cat's eye
Image Credit: Ermolaev Alexander, Shutterstock

Corneal Ulcers

Corneal Ulcers affect the cornea, the clear outer covering of the eyeball. Corneal Ulcers are usually caused by a scratch or wound to the eyeball and may create a protrusion of the third eyelid. They can quickly balloon into a severe condition that could cost your cat some or all of their eyesight in that eye, and you should ensure that a veterinarian sees your cat if you suspect they may have a corneal ulcer.


Glaucoma is a build-up of pressure inside the eyeball. It’s excruciating, and the pain from glaucoma can cause a protrusion of the third eyelid. Glaucoma is caused by the eye’s inability to properly drain the fluid from the front of the eye, causing increasing pressure build-up. This is a severe condition that needs to be diagnosed and treated by a veterinarian for the best health outcomes.

a white british shorthair cat with watery eyes discharge
Image Credit: Repelsteeltje, Shutterstock

Horner’s Syndrome

Horner’s Syndrome’s exact causes are neurological disorders that affect facial muscles. A dysfunctional nerve causes it. However, the symptom often causes the eyes to retract, appear asymmetrical and limp, and the third eyelid may be very prominent, especially in just one look.

Horner’s Syndrome may onset from a tumor or traumatic injury of the eye but can also be idiopathic. Symptoms may even clear up without any medical intervention.

Final Thoughts

There are many reasons that one might see a cat’s nictating membrane. Some of those reasons aren’t a cause for concern but use your best judgment when deciding if the visibility of your cat’s third eyelid has changed recently. Your cat’s vet will best be able to determine if your cat needs to be seen and what treatments will best keep your cat in tip-top condition.

Always consult with your vet if you have a question about your cat’s health. They have access to records about your cat’s specific case that can help them make a more informed judgment on whether or not a situation is benign.

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