Why do cats have 3 eyelids?
Jessica Wood
Updated on January 11, 2026
The exact function of the third eyelid in cats is not completely known but it is believed to help protect a very large cornea from injury as cats move through tall grass or capture prey.
third eyelid
The term comes from the Latin word nictare, meaning "to blink". It is often called a third eyelid or haw, and may be referred to in scientific terminology as the plica semilunaris, membrana nictitans, or palpebra tertia. Unlike the upper and lower eyelids, the nictitating membrane moves horizontally across the eyeball.
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