biology

Meibomian gland

Meibomian gland is a biology topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Meibomian gland rather than just read about it. In short: 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.

Key takeaways

Meibomian gland belongs to biology; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Meibomian gland to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Meibomian gland from memory before moving on to harder problems.

Reference excerpt

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.

History

The 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.

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 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. 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 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, 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 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 a commercial eyelid cleanser or baby shampoo, 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.

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

References

External links synd/541 at Whonamedit? Rethinking Meibomian Gland Dysfunction: How to Spot It, Stage It and Treat It

Illustrations

Worked examples

Example 1 — a first encounter with Meibomian gland

Start with the simplest possible case. Write down what Meibomian gland claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In biology, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Meibomian gland before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Meibomian gland ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Meibomian gland

In research: Meibomian gland appears in biology research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Meibomian gland in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Meibomian gland is common in secondary-school and first-year university syllabi. It links to neighbouring topics Anatomy named for one who described it, Human eye anatomy, so understanding it makes those chapters shorter.
In everyday life: Look for Meibomian gland outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

Ask Teacher Smith questions about this articleOpens your AI tutor with a question about “Meibomian gland” →

Affiliate

Preply — study more efficiently by working with a personal tutor. 50% off.

How to study Meibomian gland in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Meibomian gland means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Meibomian gland out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Meibomian gland in simple terms?

Why does Meibomian gland matter?

Because it connects several biology ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Meibomian gland?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Meibomian gland.