Meibomian glands (also called tarsal glands) are holocrine type exocrine 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.
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. An update[clarification needed] was published in 2009 on the composition of human meibum and on the structures of various positively identified meibomian lipids
In humans, more than 90 different proteins have been identified in meibomian gland secretions.
Dysfunctional meibomian glands often cause dry eyes, one of the more common eye conditions. They may also contribute to blepharitis. Inflammation of the meibomian glands (also known as meibomitis, meibomian gland dysfunction, or posterior blepharitis) causes the glands to be obstructed by thick, cloudy-to-yellow, more opaque and viscous-like, oily and waxy secretions, a change from the glands' normal clear 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.
Meibomian gland dysfunction is more often seen in women, and is regarded as the main cause of dry eye disease. Factors that contribute to meibomian gland dysfunction can include things such as a person's age and/or hormones, or severe infestation of Demodex brevis mite.
Treatment can include warm compresses to thin the secretions and eyelid scrubs with baby shampoo or eyelid cleanser, or emptying ("expression") of the gland by a professional. Lifitegrast and Restasis are topical medication commonly used to control the inflammation and improve the oil quality. In some cases topical steroids and topical (drops or ointment)/oral antibiotics (to reduce bacteria on the lid margin) are also prescribed to reduce inflammation. Intense pulsed light (IPL) treatments have also been shown to reduce inflammation and improve gland function. Meibomian gland probing is also used on patients who experience deep clogging of the glands.
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