Meibum

Meibomian (/mī-ˈbō-mē-ən/) glands (also called tarsal glands, palpebral glands, and tarsoconjunctival glands) are sebaceous glands along the rims of the eyelid inside the tarsal plate. They produce meibum, an oily substance that prevents evaporation of the eye's tear film. Meibum prevents tears from spilling onto the cheek, traps them between the oiled edge and the eyeball, and makes the closed lids airtight. There are about 25 such glands on the upper eyelid, and 20 on the lower eyelid. Dysfunctional meibomian glands is believed to be the most common cause of dry eyes. They are also the cause of posterior blepharitis. HistoryThe glands were mentioned by Galen in 200 AD and were described in more detail by Heinrich Meibom (1638–1700), a German physician, in his work De Vasis Palpebrarum Novis Epistola in 1666. This work included a drawing with the basic characteristics of the glands. AnatomyAlthough the upper lid has a greater number and volume of meibomian glands than the lower lid, there is no consensus whether it contributes more to the tear film stability. The glands do not have direct contact with eyelash follicles. The process of blinking releases meibum into the lid m