The third eyelid in cat, also known as the nictitating membrane, is a thin layer of tissue located at the inner corner of a cat’s eye. It serves several important functions, including protecting the eye from injury, lubricating the cornea, and removing debris from the surface of the eye.

One of the primary functions of the third eyelid is to protect the cat’s eye from injury. The nictitating membrane can quickly move across the eye to provide a barrier between the cornea and potential harm, such as dust, dirt, or even other animals. In addition, the third eyelid contains a layer of lymphoid tissue that helps to protect the eye from infection.

Another important function of the third eyelid is to lubricate the cornea. The nictitating membrane contains a gland that produces a clear, watery fluid that helps to keep the cornea moist and healthy. This is particularly important for cats that spend a lot of time in dry environments, as a lack of moisture can lead to irritation and damage to the cornea.

Finally, the third eyelid helps to remove debris from the surface of the eye. As the nictitating membrane moves across the eye, it helps to sweep away any dirt, dust, or other foreign objects that may have come into contact with the eye. This can help to prevent irritation and infection, and keep the cat’s eyes healthy and clear.

In summary, the third eyelid plays a vital role in protecting and maintaining the health of a cat’s eyes. It is an important structure that should be carefully monitored by cat owners, as any changes in the appearance or function of the nictitating membrane could indicate a potential health problem.