biology

Schlemm's canal

Schlemm's canal 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 Schlemm's canal rather than just read about it. In short: Schlemm's canal, also known as the canal of Schlemm, and as the scleral venous sinus, is a circular lymphatic-like vessel in the eye. It collects aqueous humor from the anterior chamber and delivers it into the episcleral blood vessels.

Key takeaways

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

Reference excerpt

Schlemm's canal, also known as the canal of Schlemm, and as the scleral venous sinus, is a circular lymphatic-like vessel in the eye. It collects aqueous humor from the anterior chamber and delivers it into the episcleral blood vessels. Canaloplasty may be used to widen it.

Structure Schlemm's canal is an endothelium-lined tube, resembling that of a lymphatic vessel. On the inside of the canal, nearest to the aqueous humor, it is covered and held open by the trabecular meshwork. This creates outflow resistance against the aqueous humor.

Development While Schlemm's canal has generally been considered as a vein or a scleral venous sinus, the canal is similar to the lymphatic vasculature. It is never filled with blood in physiological settings as it does not receive arterial blood circulation. Schlemm's canal displays several features of lymphatic endothelium, including the expression of PROX1, VEGFR3, CCL21, FOXC2, but lacked the expression of LYVE1 and PDPN. It develops via a unique mechanism involving the transdifferentiation of venous endothelial cells in the eye into lymphatic-like endothelial cells. This developmental morphogenesis of the canal is sensitive to the inhibition of lymphangiogenic growth factors. In adults, the administration of the lymphangiogenic growth factor VEGFC enlarged the Schlemm's canal, which was associated with a reduction in intraocular pressure. In the combined absence of angiopoietin 1 and angiopoietin 2, Schlemm's canal and episcleral lymphatic vasculature completely failed to develop.

Function Schlemm's canal collects aqueous humor from the anterior chamber. It delivers it into the episcleral blood vessels via aqueous veins.

Clinical significance

Canaloplasty Canaloplasty is a procedure to restore the eye's natural drainage system to provide sustained reduction of intraocular pressure. Microcatheters are used in a simple and minimally invasive procedure. A surgeon creates a tiny incision to gain access to Schlemm's canal. A microcatheter circumnavigates Schlemm's canal around the iris, enlarging the main drainage channel and its smaller collector channels through the injection of a sterile, viscoelastic material. The catheter is then removed and a suture is placed within the canal and tightened. By opening Schlemm's canal, the pressure inside the eye is relieved.

Laser trabeculoplasty A trabeculoplasty is a modification of the trabecular meshwork. Laser trabeculoplasty (LTP) is the application of a laser beam to burn areas of the trabecular meshwork, located near the base of the iris, to increase fluid outflow. LTP is used in the treatment of various open-angle glaucomas. The two types of laser trabeculoplasty are Argon Laser Trabeculoplasty (ALT) and Selective Laser Trabeculoplasty (SLT). As its name suggests, Argon laser trabeculoplasty uses an Argon laser to create tiny burns on the trabecular meshwork. Selective laser trabeculoplasty is newer technology that uses a laser to target specific cells within the trabecular meshwork and create less thermal damage than ALT. SLT shows promise as a long-term treatment. In SLT, a laser is used to selectively target the melanocytes in the trabecular meshwork. Though the mechanism by which SLT functions is not well understood, it has been shown in trials to be as effective as the older Argon Laser Trabeculoplasty. However, because SLT is performed using a much lower power laser, it does not appear to affect the structure of the trabecular meshwork (based on electron microscopy) to the same extent, so retreatment may be possible if the effects from the original treatment should begin wear off, although this has not been proven in clinical studies. ALT is repeatable to some extent with measurable results possible. If SLT is successful, it will stimulate metabolic change in pigmented cells in the trabecular meshwork. This causes an immune response which, in turn, clears the meshwork channel/drain of cellular build up. This allows more aqueous humour to flow into Schlemm's canal from the anterior cavity, reducing the intraocular pressure and therefore lowering the risk of glaucoma, or further damage to the optic nerve, due to overpressure in the eye.

Angiopoietin deficiency Schlemm's canal and episcleral lymphatic vasculature completely failed to develop in the combined absence of angiopoietin 1 and angiopoietin 2. This causes buphthalmos and glaucoma.

Glaucoma Glaucoma may be related to drainage of aqueous humor from the eye. This is mostly related to resistance on the internal surface of Schlemm's canal.

History Schlemm's canal is named after Friedrich Schlemm (1795–1858), a German anatomist.

Additional images

See also Intraocular pressure Ocular hypertension

References

External links Histology image: 08005loa – Histology Learning System at Boston University Diagram Diagram

Illustrations

Worked examples

Example 1 — a first encounter with Schlemm's canal

Start with the simplest possible case. Write down what Schlemm's canal 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 Schlemm's canal 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 Schlemm's canal 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 Schlemm's canal

In research: Schlemm's canal 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 Schlemm's canal 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: Schlemm's canal 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 Schlemm's canal 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.

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How to study Schlemm's canal in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Schlemm's canal 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 Schlemm's canal out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Schlemm's canal in simple terms?

Why does Schlemm's canal 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 Schlemm's canal?

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 Schlemm's canal.