Meibomian gland

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. They prevent tear spillage onto the cheek, trapping tears between the oiled edge and eyeball, and make 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.

Lipids
Lipids are the major components of meibum (also known as "meibomian gland secretions"). The term "meibum" was originally introduced by Nicolaides et al in 1981. The biochemical composition of meibum is extremely complex and very different from that of sebum. Lipids are universally recognized as major components of human and animal meibum. Recently, an update on the composition of human meibum and on the structures of various positively identified meibomian lipids was published. Currently, the most sensitive and informative approach to lipidomic analysis of meibum is mass-spectrometry in combination with liquid chromatography.

Proteins
In humans, more than 90 different proteins have been identified in meibomian gland secretions.

Dysfunction
Dysfunctional meibomian glands often cause dry eyes, one of the more common eye conditions. They may also cause blepharitis, as the dry eyeball rubs off small pieces of skin from the eyelid, which may get infected. Inflammation of the meibomian glands (also known as meibomitis, meibomian gland dysfunction, or posterior blepharitis) causes the glands to be obstructed by thick waxy secretions. Besides leading to dry eyes, the obstructions can be degraded by bacterial lipases, resulting in the formation of free fatty acids, which irritate the eyes and sometimes cause punctate keratopathy.