Cat Eye Health: What Is The Third Eyelid In Cats?

Sep 4, 2023 | Cat Behavior, Cat Health

Have you heard that your cat has a third eyelid? It’s an insane concept, but the fact is your cat has a secret eyelid that you’ve likely never seen, or at least shouldn’t be seeing. We’ll explore what the third eyelid is in cats and why it sometimes makes an appearance. We’ll also provide guidance on what to do if you see your furry friend’s third eyelid showing. Get ready to gain a better understanding of your cat’s eye health and how to care for them!

Cat’s Third Eyelid Key Takeaways

The third eyelid in cats, called the nictitating membrane, acts as a protective shield for the cornea and helps prevent corneal ulcers.

Changes in the visibility of the third eyelid may indicate underlying eye problems such as cherry eye or Horner’s syndrome.

Frequent visibility of the third eyelid can be a sign of an injury or neurological disorder affecting its movement.

Regular monitoring of the third eyelid is important for maintaining a cat’s eye health and consulting a veterinarian if it is consistently visible.

What Is Your Cat’s Third Eyelid?

Cat with third eyelid disease, protrusion of nictitating membrane

Do you know what your cat’s third eyelid does? It’s called the nictitating membrane, and it plays an important role in protecting your furry friend’s eyes. Unlike humans, cats have a visible third eyelid located in the inner corner of their eyes. This membrane acts as a shield, helping to keep debris away from their cornea and preventing corneal ulcers. Sometimes, you may notice that your cat’s third eyelid becomes more prominent or even covers part of their eye. This could indicate a condition like cherry eye, where the gland in the third eyelid pops out. Horner’s syndrome or Haw’s syndrome can also cause this. If you ever observe any changes with your cat’s eyes or notice their third eyelid staying visible for an extended period, it’s best to consult with a veterinarian who can determine if further action is needed to maintain your feline friend’s eye health.

Should You See A Cats Third Eyelid?

You can easily determine a cat’s level of relaxation by observing the visibility of their third eyelid. This extra eyelid, located in the inner corner of each eye, is normally hidden from view but becomes more visible when a cat is relaxed or sedated. Paying attention to this third eyelid is important for maintaining your cat’s eye health. If you notice that it is frequently visible, it could be a sign of underlying eye problems such as inflammation or infection. It could also indicate an injury or even a neurological disorder affecting the movement of the third eyelid. Therefore, if you consistently see your cat’s third eyelid, it’s time to bring in the big guns and get them examined for the underlying cause.

Common Reasons The Third Eyelid Of A Cat May Appear

If you ever have to take your cat to the veterinarian for an eye issue, there are a few common reasons why their third eyelid may appear:

Veterinarian placing eye drops in a cats eyes

Sedation Or Anethesia

Sedation or anesthesia can cause a partially covered eye in cats, but this should resolve within a few hours after waking. It’s important to understand that this is a normal and expected effect of the medication used during the procedure. Your cat’s eye health is your vet’s top priority, and they want to ensure that any concerns are addressed promptly. If you notice that your cat’s third eyelid remains visible beyond the day of the procedure, it may be an indication of an underlying issue and should be checked by the veterinarian. Keeping up with regular veterinary care is essential for maintaining your cat’s overall eye health. Certain conditions like conjunctivitis or even cat flu can also lead to ocular surface issues, so it’s always best to seek professional advice if you have any concerns about your cat’s eyes.


Corneal Ulcers

Corneal ulcers can be caused by various sources, such as scrapes, scratches, puncture wounds, or irritating substances. These ulcers are injuries to the cornea that can cause pain and inflammation in your cat’s eye. In severe cases, you may notice the third eyelid appearing. It’s important to prioritize your cat’s eye health and seek veterinary treatment promptly if you suspect a corneal ulcer. If left untreated, these ulcers can quickly become serious and lead to further complications. A feline ophthalmologist will perform diagnostic tests to determine the cause of the ulcer. This may involve examining your cat’s eye for foreign bodies or signs of viral infection. Treatment often involves using various eye medications and possibly oral medications as well. Remember to keep an eye out for any changes in your cat’s behavior or appearance of their eyes, such as eye discharge or inflammation of the conjunctiva. By being proactive in monitoring your cat’s eye health and seeking timely veterinary care when needed, you can ensure their overall well-being.



Glaucoma causes pressure to build up in your cat’s eye and can lead to optic nerve damage if left untreated. This condition can be quite painful for your furry friend, so it’s important to seek help from a cat eye doctor as soon as possible. One visible sign of glaucoma is the elevation or protrusion of the third eyelid. You may notice that your cat’s third eyelid appears swollen or bulging outwards. This bilateral third eyelid protrusion is often accompanied by redness and discomfort in the affected eye. It’s crucial to address this issue promptly because glaucoma can progress rapidly and potentially result in permanent vision loss. If you observe any changes in your cat’s eyes, especially a protruding third eyelid, don’t hesitate to consult a veterinarian who specializes in feline eye health as soon as possible as early intervention is key when it comes to preserving your beloved pet’s vision.



If left untreated, uveitis can lead to serious complications and discomfort for your feline friend. Uveitis is the inflammation of the uvea, a crucial part of the eyeball that contains numerous blood vessels. This condition causes the eyes to appear red and can cause pain in cats. Additionally, many cases of uveitis also involve inflammation of the third eyelid in cats. The third eyelid is a protective membrane located at the inner corner of their eyes. It helps shield their delicate eyes from debris and injury. Regular monitoring of your cat’s eye health is essential to catch any signs of uveitis early on. If you notice any redness or discomfort in your cat’s eyes, it’s vital to seek veterinary care promptly to prevent further complications.


Cherry Eye

You may notice a swollen gland in the inner corner of your feline friend’s eye, which is commonly referred to as ‘cherry eye’. This condition affects the third eyelid of cats and can be a concerning health issue. The third eyelid serves to protect the delicate surface of the eye. When the gland within this eyelid becomes inflamed or enlarged, it can cause cherry eye. While cherry eye is relatively uncommon in most cats, certain breeds like Burmese cats are more prone to developing this condition. The exact causes of cherry eye are not fully understood, but it is believed to involve genetic factors and weak connective tissues. Surgical intervention is often recommended to treat cherry eye and restore your cat’s optimal eye health.


Sleepiness Or Relaxed State

When your cat is very relaxed or tired, their third eyelids may become visible. This is a normal occurrence and nothing to be alarmed about. The third eyelid, also known as the nictitating membrane, helps protect your cat’s eyes from dust and debris. It acts as an extra layer of defense for their delicate eyes. When you see the third eyelid showing, it means that your cat is in a state of deep relaxation or sleepiness. It’s actually quite fascinating to take a close look at this inner eyelid and observe how it functions. However, if the third eyelid remains visible for longer than usual or appears swollen or inflamed, it could be indicative of an underlying health issue that requires veterinary attention.



Conjunctivitis, commonly known as ‘pink eye,’ is an inflammation of the thin mucous membrane that covers the front part of your eye and lines the inside of your eyelids. It can occur due to infections, allergies, injuries, or irritants in your environment. If you notice redness, itching, or a discharge in the inside corner of your eye, it could be a sign of conjunctivitis. Cats can also experience this condition with symptoms like inflammation and protrusion of their third eyelid. Conjunctivitis can sometimes be caused by tall grass or other allergens that come into contact with your eyes. In mild cases, conjunctivitis may resolve on its own or with simple home care like warm compresses and gentle cleaning. However, in more severe cases where bacterial infection is present, medication such as antibiotics may be necessary to clear the infection and reduce inflammation. It’s important to avoid touching or rubbing the eyes excessively as this can worsen the condition or introduce further irritants.


Horner’s Syndrome

Horner’s syndrome is a neurological disorder that can cause asymmetrical eyes and a droopy eyelid on one side of the face. This condition affects cat eye health and can be distressing for both you and your feline friend. The third eyelid plays an important role in protecting your cat’s eyes from foreign objects and bright light. In some cases of Horner’s syndrome, this third eyelid may become more prominent or prolapse due to the dysfunction of nerves that control the facial muscles. It’s essential to consult with a veterinarian if you notice any changes in your cat’s face or eyes. They may recommend eye medications or further tests to determine the underlying cause, which could involve issues with the optic nerve or other neurological factors.


Eye Growths

If you notice any unusual swelling or growth in your feline friend’s eye, it’s important to contact your vet right away. One possible cause for such growth is the protrusion of the third eyelid, also known as nictitating membrane. Although this transparent eyelid usually remains hidden, it can become visible when there are eye issues or inflammation. Eye growths can occur due to various reasons including tumors, cysts, or foreign material. They may be benign or malignant and can affect both eyes simultaneously. Some primary eye conditions that could lead to these growths include feline calicivirus infection and upper respiratory infections. It’s crucial to seek veterinary assistance promptly as these growths can cause discomfort and may even result in watery diarrhea if left untreated. Your veterinarian will conduct a thorough examination and provide the necessary treatment plan for your cat’s eye health.

What To Do If Your Cats Third Eyelid Is Showing

Vet doctor examining pet cat eyes

When your cat’s third eyelid is showing, it’s important to seek advice from a veterinarian. The third eyelid should normally remain hidden in the corner of the eye. However, if it becomes visible, it may be a sign of illness or injury. Excessive blinking or squinting, redness, swelling, or discharge are also indicators that something is wrong with your furry friend’s eyes. While sometimes the third eyelid can appear during deep sleep and disappear when they wake up, you should not ignore its presence for an extended period. Bilateral prolapse of the third eyelid can be a common problem caused by facial nerve paralysis or traumatic injuries. To ensure good luck with your cat’s eye health, consult a veterinarian or ophthalmologist immediately for proper diagnosis and treatment options.

Cat’s Third Eyelid Frequently Asked Questions

Can Cats See Through Their Third Eyelid?

Yes, cats can see through their third eyelid. It acts as a protective layer that helps keep their eyes safe from harm. So, don’t worry, your furry friend’s vision is not compromised!


How Can I Tell if My Cat’s Third Eyelid Is Healthy?

To tell if your cat’s third eyelid is healthy, observe for any visible signs of inflammation, discharge, or changes in color. If you notice any abnormalities, consult with a veterinarian for further evaluation and treatment options.


Can a Cat’s Third Eyelid Be Removed or Surgically Corrected?

Yes, a cat’s third eyelid can be surgically removed or corrected if necessary. However, it is important to consult with a veterinarian to determine the best course of action for your cat’s specific situation.


Are There Any Long-Term Effects if a Cat’s Third Eyelid Is Constantly Showing?

If your cat’s third eyelid is constantly showing, it could indicate a health issue. It’s important to consult with a veterinarian to determine the cause and any potential long-term effects on your cat’s eye health.


Are There Any Preventive Measures to Keep a Cat’s Third Eyelid From Showing?

To prevent a cat’s third eyelid from showing, make sure they have a healthy diet and regular check-ups. Keep their eyes clean and free from infection by gently wiping them with a damp cloth.

Woman cleaning eye boogers from her cats eyes with a soft cloth with warm water

The Tail End

So, now you know all about your cat’s third eyelid! It’s a fascinating and important part of their eye health. If you ever notice your cat’s third eyelid showing, it could be a sign of an underlying issue that needs attention. Remember to always monitor your cat’s eyes closely and consult with a veterinarian if you have any concerns. Taking care of their eyes is crucial in ensuring their overall well-being.


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