The
meibomian glands (or
tarsal glands) are a special kind of
sebaceous gland at the rim of the
eyelids inside the
tarsal plate, responsible for the supply of meibum, an oily substance that prevents evaporation of the
eye's tear film. Meibum prevents tear spillage onto the cheek, trapping tears between the oiled edge and the eyeball, and makes the closed lids airtight. There are approximately 50 glands on the upper eyelids and 25 glands on the lower eyelids.