The meibomian glans (or tarsal glands) are a special kind of sebaceous glands at the rim of the eyelids, responsible for the supply of sebum, an oily substance that prevents evaporation of the eye's tear film, prevents tear spillage onto the cheek, and makes the closed lids airtight. There are approximately 50 glands on the upper eyelids and 25 glands on the lower eyelids. The glands are named after Heinrich Meibom (1638-1700), a German physician.