Cats have a third eyelid, called the nictitating membrane, in the inner corner of each eye. It’s usually hidden, but you may notice it when your cat is sleepy or relaxed. If you can see it when your cat is awake and alert, it can be a sign that something is wrong.
What Is the Third Eyelid?
The third eyelid is a thin, pale membrane that sweeps diagonally across the eye from the inner corner. It helps protect the eye, spreads tears and contains a gland that produces part of the tear film. Normally, it’s tucked away and you barely see it, except perhaps briefly when your cat is waking up, sleepy or blinking.
Why Is My Cat’s Third Eyelid Showing?
If the third eyelid stays visible in one or both eyes, possible causes include:
- eye pain or irritation, such as conjunctivitis, a scratch on the eye, or something stuck in or behind the eye (read more about watery eyes in cats);
- cat flu and other infections (read more about cat flu);
- dehydration or weight loss, which can make the eyes sit deeper in their sockets;
- general illness, including digestive problems: a common, usually temporary condition called “Haw’s syndrome” causes both third eyelids to show, often with diarrhea;
- nerve problems, such as Horner’s syndrome, in which one third eyelid shows along with a small pupil and a drooping upper eyelid;
- an injury, swelling or growth affecting the eye.
When to See the Vet
If your cat’s third eyelid is visible for more than a few hours, see your vet, especially if:
- only one eye is affected;
- your cat is squinting, pawing at its eye or the eye is red, cloudy or has discharge;
- your cat seems unwell, isn’t eating or has diarrhea or vomiting;
- you notice a change in the size of the pupils, a drooping eyelid or a head tilt.
Your vet will examine your cat’s eyes and general health to find the cause and recommend the right treatment.
Don’t try to push the third eyelid back yourself, and don’t put any drops, ointments or home remedies in your cat’s eyes unless your vet prescribes them.
