Meibomian gland

File:Meibomian gland by heinrich meibom.png. Year 1666.]]

The glands were mentioned by Galen in 200 AD{{Cite journal|title=The International Workshop on Meibomian Gland Dysfunction: Report of the Subcommittee on Anatomy, Physiology, and Pathophysiology of the Meibomian Gland|year=2011|first1=Erich|last1=Knop |first2=Nadja |last2=Knop|first3=Thomas |last3=Millar|first4=Hiroto|last4=Obata|first5=David A.|last5=Sullivan|journal=Investigative Ophthalmology & Visual Science|volume=52|issue=4|pages=1938–1978|doi=10.1167/iovs.10-6997c|pmid=21450915|pmc=3072159}} 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.{{Cite web|url=https://eyewiki.aao.org/Meibomian_Gland_Dysfunction_(MGD)|title=Meibomian Gland Dysfunction (MGD) - EyeWiki|website=eyewiki.aao.org}}{{cite book |last1=Meibomii |first1=Henrici |title=De vasis palpebrarum novis epistola … |trans-title=From a recent letter on the eyelids' vesicles to the most renowned gentleman Dr. Joel Langelott, court physician of the most reverend and serene Duke of Holstein |date=1666 |publisher=Henning Muller |location=Helmstadt, (Germany) |url=https://archive.org/details/b31623839/page/n3/mode/2up |language=la}}

Although the upper lid have greater number and volume of meibomian glands than the lower lid, there is no consensus whether it contributes more to the tearfilm stability. The glands do not have direct contact with eyelash follicles. The process of blinking releases meibum into the lid margin.{{cite journal |title=The International Workshop on Meibomian Gland Dysfunction: Executive Summary. |journal=Investigative Ophthalmology & Visual Science |author1=Kelly K. Nichols |author2=Gary N. Foulks |author3=Anthony J. Bron |author4=Ben J. Glasgow |author5=Murat Dogru |author6=Kazuo Tsubota |author7=Michael A. Lemp |author8=David A. Sullivan | year=2011 |volume=52 |issue=4 |pages=1922–1929 |doi=10.1167/iovs.10-6997a |pmid=21450913 |pmc=3072157 }}

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.{{cite journal | last1 = Nicolaides | first1 = N | last2 = Kaitaranta | first2 = JK | last3 = Rawdah | first3 = TN | last4 = Macy | first4 = JI | last5 = Boswell | first5 = FM | last6 = Smith | first6 = RE | date = April 1981 | title = Meibomian gland studies: comparison of steer and human lipids | journal = Invest Ophthalmol Vis Sci | volume = 20 | issue = 4| pages = 522–536 | pmid = 7194326 }}

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{{clarify|date=December 2020}} was published in 2009 on the composition of human meibum and on the structures of various positively identified meibomian lipids.{{Cite journal|author=Butovich IA|title=The Meibomian puzzle: combining pieces together|journal=Prog Retin Eye Res|date =November 2009|issue=6|volume=28|pages=483–498|pmid=19660571|doi=10.1016/j.preteyeres.2009.07.002|pmc=2783885}}

Currently, the most sensitive and informative approach to lipidomic analysis of meibum is mass spectrometry, either with direct infusion{{cite journal | last1 = Chen | first1 = J |last2 = Green-Church | first2 = K |last3 = Nichols | first3 = K | year = 2010 | title = Shotgun lipidomic analysis of human meibomian gland secretions with electrospray ionization tandem mass spectrometry| url =http://iovs.arvojournals.org/article.aspx?articleid=2126387 | journal = Invest Ophthalmol Vis Sci | volume = 51 | issue = 12| pages = 6220–6231 | pmid = 20671273 | doi=10.1167/iovs.10-5687 | pmc=3055753}}{{cite journal | last1 = Chen | first1 = J | last2 = Nichols | first2 = K | year = 2018 | title = Comprehensive shotgun lipidomics of human meibomian gland secretions using MS/MSall with successive switching between acquisition polarity modes| url =http://www.jlr.org/content/59/11/2223.short | journal = J Lipid Res | volume = 59 | issue = 11| pages = 2223–2236 | pmid = 30279222 | doi=10.1194/jlr.D088138 |doi-access=free | pmc=6210907}} or in combination with liquid chromatography.{{cite journal | last1 = Butovich | first1 = IA | journal = Journal of Lipid Research | title = Comprehensive shotgun lipidomics of human meibomian gland secretions using MS/MSall with successive switching between acquisition polarity modes| series = Methods Mol Biol | date = 2018 | volume = 579 | issue = 11 | pages = 221–246 | pmid = 19763478 | doi=10.1194/jlr.D088138 | doi-access = free | pmc = 6210907 }}

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.

In humans, more than 90 different proteins have been identified in meibomian gland secretions.{{cite journal | last1 = Tsai | first1 = PS | last2 = Evans | first2 = JE | last3 = Green | first3 = KM | last4 = Sullivan | first4 = RM | last5 = Schaumberg | first5 = DA | last6 = Richards | first6 = SM | last7 = Dana | first7 = MR | last8 = Sullivan | first8 = DA | date = March 2006 | title = Proteomic analysis of human meibomian gland secretions | journal = Br J Ophthalmol | volume = 90 | issue = 3| pages = 372–7 | doi = 10.1136/bjo.2005.080846 | pmid = 16488965 | pmc=1856970}}

{{Main|Meibomian gland dysfunction}}

File:Meibomian-glands.png

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.{{Cite journal |title=Meibomian gland disease: the role of gland dysfunction in dry eye disease |first1=Priyanka|last1=Chhadva |first2=Raquel|last2=Goldhardt |first3=Anat|last3=Galor |date=24 November 2017 |journal=Ophthalmology |volume=124 |issue=11 Suppl |pages=S20–S26 |doi=10.1016/j.ophtha.2017.05.031 |pmid=29055358 |pmc=5685175}}{{Cite book |author1=Peter Bex |author2=Reza Dana |author3=Linda Mcloon |author4=Jerry Niederkorn |date=2011 |url=https://books.google.com/books?id=Jr1dBAKMM-cC&dq=%22meibomian+gland+dysfunction%22&pg=PA98 |title=Ocular Periphery and Disorders |publisher=Academic Press |via=books.google.com |isbn=9780123820426 |access-date=2023-10-30}} 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.{{cite web |url=http://www.revophth.com/content/d/dry_eye/c/36944 |title=Managing and Making Sense of MGD |publisher=Review of Ophthalmology |date=2012 |access-date=26 February 2014}}{{cite web |url=http://www.aao.org/publications/eyenet/201107/cornea.cfm |title=Rethinking Meibomian Gland Dysfunction: How to Spot It, Stage It and Treat It |publisher=American Academy of Ophthalmology |date=2014 |access-date=26 February 2014}} Factors that contribute to meibomian gland dysfunction can include things such as a person's age and/or hormones,{{cite web |url=https://www.aaopt.org/mdl/meeting/AttachmentViewer?id=10540 |title=The Role of Meibomian Gland Dysfunction and Lid Wiper Epitheliopathy in Dry Eye Disease |publisher=American Academy of Optometry |date=2012 |access-date=26 February 2014 |url-status=dead |archive-url=https://web.archive.org/web/20131009132625/http://www.aaopt.org/mdl/meeting/AttachmentViewer?id=10540 |archive-date=9 October 2013 |df=dmy-all }} or severe infestation of Demodex brevis mite.

Treatment can include warm compresses to thin the secretions and eyelid scrubs with a commercial eyelid cleanser or baby shampoo,{{Cite journal|title=Efficacy of baby shampoo and commercial eyelid cleanser in patients with meibomian gland dysfunction|first1=Orapan|last1=Aryasit|first2=Yuwarat|last2=Uthairat|first3=Penny|last3=Singha|first4=Orasa|last4=Horatanaruang|date=8 May 2020|journal=Medicine|volume=99|issue=19|pages=e20155|doi=10.1097/MD.0000000000020155|pmid=32384504|pmc=7220370}} or emptying ("expression") of the gland by a professional. Lifitegrast and ciclosporin 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.

Meibomian gland dysfunction may be caused by some prescription medications, notably isotretinoin. A blocked meibomian gland can cause a chalazion (or "meibomian cyst") to form in the eyelid.

• Gland of Zeis
• List of specialized glands within the human integumentary system
• Meibomian gland dysfunction
• Moll's gland

{{Reflist}}

• {{WhoNamedIt|synd|541}}
• [http://www.aao.org/publications/eyenet/201107/cornea.cfm Rethinking Meibomian Gland Dysfunction: How to Spot It, Stage It and Treat It]

{{Accessory organs of the eye}}

{{Glands}}

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Category:Human eye anatomy

Category:Anatomy named for one who described it