Cats actually have three eyelids instead of two the third being called the nictitating membrane or palpebra tertia. This is a tiny triangle of pink tissue also called “haw”. Each time a cat blinks, her third eyelid sweeps across the corneas under the eyelids like a windshield wiper to clear off pollen, dust and debris.
Aa lacrimal gland at the base of this third eyelid produces up to 50% of normal tears. This eyelid also moistens the eye while maintaining vision and retracts into the inner corner of each eye. Most importantly, it functions as a shield while cats move through tall grass, during catfights and while pursuing a resistant prey.
The nictitating membrane is not usually seen as it is hidden from view when it is retracted in the corner of your cat’s eye. It can be seen when a cat is very relaxed, if she just woke up from a deep slumber or after being sedated due to a surgical procedure. Other animals that also have this third eyelid include birds, camels, reptiles, sharks, llamas and dogs.
The third eyelid moves so fast that it is easy to miss. Itt probably developed when cats were kept as human companions in the Middle East where sand is regularly blown by strong winds. The third membrane could be an adaptation to protect a cat’s eyes while still allowing it to see to a certain degree due to the thin membrane.
Why does my cat’s second eyelid show?
These are the probable reasons why your nictitating membrane is showing or will prolapse although your cat is already alert:
- due to eye diseases such as inflammation in one or both eyes
- your cat has a high body temperature or fever
- your cat is dehydrated
- nerve damage in the face and neck
- due to intestinal upset such as worms or parasites, food intolerance or viral and bacterial gut infection
- due to trauma like corneal ulcer
- your cat has conjunctivitis or feline upper respiratory virus
How many eyelids does a cat have?
Cats have an additional third eyelid called the nictitating membrane aside from the normal upper and lower eyelids. This translucent third eyelid moves diagonally across the eye starting from its inner corner. It is scientifically called the palpebra tertia and also referred to as the “haw”.
Do all cats have second eyelids?
All cats not only have second eyelids but also a third eyelid called the nictitating membrane. It is whitish-pink in color and located under the other eyelids in the eye’s inner corner. Aside from cats, other mammals such as seals, camels, polar bears and aardvarks have this membrane as well as birds, amphibians and reptiles.
What does a cat’s 3rd eyelid look like?
A cat’s third eyelid or nictitating membrane is a translucent fold of tissue protruding in the bottom inner corner of the eye which sets it apart from the first or upper and second or lower eyelid. It also protrudes if you try to pull up the upper or first eyelid. This eyelid is covered in conjunctiva, the same tissue on the white of the eye and it keeps its shape with the help of special T-shaped cartilage.
What do I do if my cat’s third eyelid is showing?
If your cat’s third eyelid is showing due to a catfight or foreign object gently separate the eyelids and place saline solution between the lids. If there is bleeding cover the area with a nonstick pad, secure with a bandage tape and bring the cat to the vet. It could also be showing due to health concerns such as eye disease, fever or nerve damage. Bring your cat to the vet for the proper diagnosis and treatment.
You can also check out our earlier article on do cats see in color or black and white for more information about a cat’s eyes.
Cats largely depend on their sense of sight for hunting and finding their way around. Aside from their upper and lower eyelids they also have a third eyelid called the nictitating membrane. It serves as a windshield wiper to protect their eyes from dust, pollen and dirt and to shield them during catfights, from tall grass and when pursuing resistant prey.
Image: istockphoto.com / smirart