What is a cat’s third eyelid?

Cat‘s Third Eyelid Did you know that cats have more than two eyelids per eye? In addition to the upper and lower eyelids, there is a third eyelid that you don’t usually see. In some cases, a protruding third eyelid is actually a sign of disease or injury. What is a cat’s third eyelid? Cats and many other mammals have a third eyelid, called the nictitating membrane. The membrane is located at the corner of each eye, towards the center of the face. The third eyelid is usually retracted and invisible. Certain conditions may cause the third eyelid to protrude and partially cover the eyeball. Causes of a Cat’s Third Eyelid Appearance It is not common to see a cat’s third eyelid. In many cases, the appearance of the third eyelid indicates a problem. There are several reasons for a cat’s third eyelid to protrude. Some are considered normal, while others are problematic. In general, you should contact your veterinarian if you notice that your cat’s third eyelid is protruding for more than a few hours.

1. Sleepy or relaxed state It is normal for a part of the third eyelid to appear when the cat is very relaxed or tired. You may notice that the third eyelid is raised when your cat is sleeping or just waking up. Once the cat is awake and alert, the third eyelid should be retracted. If the third eyelid stays longer than
2. Sedation or Anesthesia If your cat is under anesthesia or sedation during a medical procedure, the third eyelid will appear and partially cover the eye due to the extreme relaxation of the body. The effects may last for a few hours upon waking, but should wear off gradually. This is considered normal and not a problem unless the third eyelid is still up on the day of surgery.
3. Conjunctivitis The conjunctiva is a thin, transparent mucous membrane that lines the inside of the eyelids and covers the front of the eye. Sometimes called “pink eye,” conjunctivitis simply means inflammation of the conjunctiva. It can be caused by infection, allergies, injury or eye irritants. It is not uncommon for conjunctivitis to cause inflammation and protrusion of the third eyelid. Cats with conjunctivitis are usually treated with medicated eye drops or ointment containing antibiotics and/or steroids.
4. Corneal ulcers The cornea is transparent and covers the front of the eye, including the iris and pupil. Corneal ulcers are wounds in the cornea that can cause pain and inflammation in the eye and may cause the third eyelid to appear. Corneal ulcers are usually caused by eye injuries, such as abrasions, scratches, or punctures. Irritating or abrasive substances can also cause corneal ulcers. Corneal ulcers can quickly become very serious and require veterinary treatment. Cats with corneal ulcers usually require one or more eye medications and may also require oral medications.
5. Uveitis The uvea is the middle part of the eye and contains many blood vessels. Inflammation of the uvea is called uveitis. It often makes the eyes look red and sometimes painful. The third eyelid may or may not be affected.
6. Glaucoma Glaucoma is a painful eye condition that causes increased pressure inside the eye. This is because the aqueous humor (fluid in the front of the eye) cannot drain properly. Excessive stress can cause damage to the optic nerve and can lead to blindness. Inflammation of the third eyelid can sometimes accompany glaucoma.
7. Cherry eye The third eyelid contains a gland that swells and looks like a rounded protrusion at the inner corner of the eye. This is called nictitating membrane prolapse or cherry eye. It is relatively uncommon in most cats, but is common in Burmese cats. Surgery is the treatment for cherry eye.
8. Eye Growth Growths, tumors, lumps, and cysts in and around the eye can cause inflammation and protrusion of the third eyelid. If you notice unusual growth or swelling in or around your cat’s eye, contact your veterinarian to avoid further trouble.
9. Horner syndrome Horner syndrome is a neurological disorder caused by neurological dysfunction. It affects the eyes and facial muscles, making the eyes appear asymmetrical. The third eyelid is usually very prominent in one eye. The eyelids are droopy and the eyes themselves look “inward”. Horner syndrome can be caused by trauma or a tumor, but sometimes the cause cannot be determined. This situation may resolve itself. What if you see a cat’s third eyelid? If you notice that your cat’s eyelids are bulging and it doesn’t seem to be caused by sleep, relaxation, sedation, or anesthesia, it could mean a medical problem. Contact your veterinarian as soon as possible for advice. If your cat is showing other signs of illness, it is best to have your cat see a veterinarian for a checkup. Do not try to put anything in your eyes without veterinary advice as this can make things worse. Eye problems can easily get worse, so don’t delay and see a veterinarian as soon as possible.