Meibom's glands are specialised sebaceous glands located in the thickness of the tarsus (cartilage) of the upper and lower eyelids, whose outlets open along the posterior edge of the eyelid margin just behind the lash line. In each eyelid there are approximately 25-40 Meibom's glands in the upper eyelid and 20-30 in the lower eyelid, arranged vertically and parallel to each other, forming a characteristic pattern visible on transilluminating examination of the eyelids (meibography). These glands are holocrine glands, meaning that secretion occurs by the breakdown of whole lipid-filled epithelial cells, which accumulate in the central duct of the gland and are released onto the surface of the eyelid margin during blinking. Meibom's glands produce meibum, a complex mixture of lipids (mainly wax esters, cholesterol esters, triacylglycerols and free fatty acids) of an oil-like nature, which forms the outer, lipid layer of the tear film.
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