Often called a third eyelid or haw, it may be referred to in scientific terminology as the "plica semilunaris", "membrana nictitans" or "palpebra tertia".
The duct empties into the nasal cavity middle nasal meatus through the infundibulum of the hiatus semilunaris.
With ocular allergies, the lacrimal caruncle and plica semilunaris may be inflamed and pruritic (itchy) due to histamine release in the tissue and tear film.
These occur throughout the conjunctiva, especially the plica semilunaris.
