Meibomian glands (also called tarsal glands, palpebral glands, and tarsoconjunctival glands) are

sebaceous gland A sebaceous gland or oil gland is a microscopic exocrine gland in the skin that opens into a hair follicle to secrete an oily or waxy matter, called sebum, which lubricates the hair and skin of mammals. In humans, sebaceous glands occur in ...

s along the rims of the

eyelid An eyelid ( ) is a thin fold of skin that covers and protects an eye. The levator palpebrae superioris muscle retracts the eyelid, exposing the cornea to the outside, giving vision. This can be either voluntarily or involuntarily. "Palpebral ...

inside the tarsal plate. They produce meibum, an oily substance that prevents evaporation of the eye's

tear film Tear, tears or tearing may refer to: * Tearing, the act of breaking apart a material by force * Tears, a clear liquid secreted by the tear gland in the eyes of land mammals Arts and entertainment Literature * "Tears", a poem by Edward Thomas ...

. Meibum prevents

tears Tears are a clear liquid secreted by the lacrimal glands (tear gland) found in the eyes of all land mammals. Tears are made up of water, electrolytes, proteins, lipids, and mucins that form layers on the surface of eyes. The different types of ...

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 often cause of

dry eye Dry eye syndrome, also known as keratoconjunctivitis sicca, is the condition of having dry eyes. Symptoms include dryness in the eye, irritation, redness, discharge, blurred vision, and easily fatigued eyes. Symptoms range from mild and occas ...

s. They are also the cause of posterior blepharitis.

History

The glands were mentioned by

Galen Aelius Galenus or Claudius Galenus (; September 129 – AD), often Anglicization, anglicized as Galen () or Galen of Pergamon, was a Ancient Rome, Roman and Greeks, Greek physician, surgeon, and Philosophy, philosopher. Considered to be one o ...

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.

Anatomy

Although 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 margin.

Function

Meibum

Lipids

Lipid Lipids are a broad group of organic compounds which include fats, waxes, sterols, fat-soluble vitamins (such as vitamins A, D, E and K), monoglycerides, diglycerides, phospholipids, and others. The functions of lipids include storing ...

s 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 A sebaceous gland or oil gland is a microscopic exocrine gland in the skin that opens into a hair follicle to secrete an oily or waxy matter, called sebum, which lubricates the hair and skin of mammals. In humans, sebaceous glands occur ...

. Lipids are universally recognized as major components of human and animal meibum. An update was published in 2009 on the composition of human meibum and on the structures of various positively identified meibomian lipids. Currently, the most sensitive and informative approach to lipidomic analysis of meibum is

mass spectrometry Mass spectrometry (MS) is an analytical technique that is used to measure the mass-to-charge ratio of ions. The results are presented as a ''mass spectrum'', a plot of intensity as a function of the mass-to-charge ratio. Mass spectrometry is used ...

, either with direct infusion or in combination with liquid chromatography. The lipids are the main component of the lipid layer of the tear film, preventing rapid evaporation and it is believed they lower the surface tension which helps to stabilize the tear film.

Proteins

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

Clinical significance

Dysfunctional meibomian glands often cause

s, one of the more common eye conditions. They may also contribute to

blepharitis Blepharitis, sometimes known as granulated eyelids, is one of the most common ocular conditions characterized by inflammation, scaling, reddening, and crusting of the eyelid. This condition may also cause swelling, burning, itching, or a grainy ...

. 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

lipase In biochemistry, lipase ( ) refers to a class of enzymes that catalyzes the hydrolysis of fats. Some lipases display broad substrate scope including esters of cholesterol, phospholipids, and of lipid-soluble vitamins and sphingomyelinases; howe ...

s, resulting in the formation of free

fatty acid In chemistry, in particular in biochemistry, a fatty acid is a carboxylic acid with an aliphatic chain, which is either saturated and unsaturated compounds#Organic chemistry, saturated or unsaturated. Most naturally occurring fatty acids have an ...

s, 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 ''Demodex brevis'' is one of the two species of face mite that inhabit humans (the other being ''Demodex folliculorum''). They are about half as long, at 0.15 to 0.2 mm (6 to 8 thousandths of an inch), as ''D. folliculorum'', but otherwise ...

mite. Treatment can include warm compresses to thin the secretions and eyelid scrubs with a commercial eyelid cleanser or baby shampoo, or emptying ("expression") of the gland by a professional. Lifitegrast and

ciclosporin Ciclosporin, also spelled cyclosporine and cyclosporin, is a calcineurin inhibitor, used as an immunosuppressant medication. It is taken Oral administration, orally or intravenously for rheumatoid arthritis, psoriasis, Crohn's disease, nephr ...

are topical medication commonly used to control the inflammation and improve the oil quality. In some cases, topical

steroid A steroid is an organic compound with four fused compound, fused rings (designated A, B, C, and D) arranged in a specific molecular configuration. Steroids have two principal biological functions: as important components of cell membranes t ...

s and topical (drops or ointment)/oral

antibiotic An antibiotic is a type of antimicrobial substance active against bacteria. It is the most important type of antibacterial agent for fighting pathogenic bacteria, bacterial infections, and antibiotic medications are widely used in the therapy ...

s (to reduce bacteria on the lid margin) are also prescribed to reduce inflammation.

Intense pulsed light Intense pulsed light (IPL) is a technology used by cosmetic and medical practitioners to perform various skin treatments for aesthetic and therapeutic purposes, including hair removal, photorejuvenation (e.g. the treatment of skin pigmentation, ...

(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. Meibomian gland dysfunction may be caused by some prescription medications, notably

isotretinoin Isotretinoin, also known as 13-''cis''-retinoic acid and sold under the brand name Accutane among others, is a medication used to treat skin diseases like harlequin-type ichthyosis, and lamellar ichthyosis, and severe cystic acne or moderat ...

. A blocked meibomian gland can cause a

chalazion A chalazion (; plural chalazia or chalazions) or meibomian cyst is not a cyst but a granuloma in the eyelid that results from a blocked meibomian gland. It typically occurs in the middle of the eyelid, red, and not painful. They tend to come ...

(or "meibomian cyst") to form in the eyelid.

References

External links

*
Rethinking Meibomian Gland Dysfunction: How to Spot It, Stage It and Treat It
{{Authority control Human eye anatomy Anatomy named for one who described it