Schlemm's canal

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Schlemm's canal
Blausen 0390 EyeAnatomy Sectional.png
Anterior part of the human eye, with Canal of Schlemm at lower right.
The upper half of a sagittal section through the front of the eyeball. (Canal of Schlemm labeled at center left.)
Latin sinus venosus sclerae
Gray's p.1005
TA A12.3.06.109
FMA 51873
Anatomical terminology

Schlemm's canal, also known as canal of Schlemm or the scleral venous sinus, is a circular channel in the eye that collects aqueous humor from the anterior chamber and delivers it into the bloodstream via the anterior ciliary veins.[1] It is named after Friedrich Schlemm (1795–1858), a German anatomist.

The canal is essentially an endothelium-lined tube, resembling that of a lymphatic vessel. On the inside of the canal, nearest to the aqueous humor, it is covered by the trabecular meshwork, this region makes the greatest contribution to outflow resistance of the aqueous humor.

While Schlemm's canal has been considered a scleral venous sinus and the eye an immune-privileged organ, three recent independently made studies led by Aleksanteri Aspelund and Kari Alitalo from the University of Helsinki, Dae-Young Park and Gou Young Koh from KAIST and Krishnakumar Kizhatil and Simon W. M. John from the Howard Hughes Medical Institute, discovered that Schlemm's canal displays several features of lymphatic endothelium and develops via a unique mechanism involving the transdifferentiation of venous endothelial cells in the eye into lymphatic-like endothelial cells.[2][3][4]

Role in glaucoma[edit]

The canal transfers approximately 2-3 microliters of aqueous humor per minute.[5] If debris builds up, due to infection or injury in the aqueous humor, the canal is blocked and ocular hypertension is the result.


Canaloplasty is an advanced, nonpenetrating procedure designed to enhance and restore the eye’s natural drainage system to provide sustained reduction of intraocular pressure. Canaloplasty utilizes microcatheters in a simple and minimally invasive procedure. To perform a canaloplasty, a surgeon will create 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, gel-like material called viscoelastic. The catheter is then removed and a suture is placed within the canal and tightened. By opening Shlemm's canal, the pressure inside the eye is relieved. Long-term results are available, published in May 2009 in the Journal of Cataract and Refractive Surgery.[6][7][8][9]

Additional images[edit]

See also[edit]


  1. ^ Cassin, B. and Solomon, S. Dictionary of Eye Terminology. Gainesville, Florida: Triad Publishing Company, 1990.
  2. ^ Aleksanteri Aspelund, Tuomas Tammela, Salli Antila, Harri Nurmi, Veli-Matti Leppänen, Georgia Zarkada, Lukas Stanczuk, Mathias Francois, Taija Mäkinen, Pipsa Saharinen, Ilkka Immonen, and Kari Alitalo. (2014). "The Schlemm's canal is a VEGF-C/VEGFR-3-responsive lymphatic-like vessel.". The Journal of Clinical Investigation. doi:10.1172/JCI75395. PMID 25061878. 
  3. ^ Dae-Young Park, Junyeop Lee, Intae Park, Dongwon Choi, Sunju Lee, Sukhyun Song, Yoonha Hwang, Ki Yong Hong, Yoshikazu Nakaoka, Taija Makinen, Pilhan Kim, Kari Alitalo, Young-Kwon Hong, and Gou Young Koh (2014). "The Schlemm's canal is a VEGF-C/VEGFR-3-responsive lymphatic-like vessel.". The Journal of Clinical Investigation. doi:10.1172/JCI75392. PMID 25061877. 
  4. ^ Krishnakumar Kizhatil, Margaret Ryan, Jeffrey K. Marchant, Stephen Henrich, Simon W. M. John (2014). "Schlemm's canal is a unique vessel with a combination of blood vascular and lymphatic phenotypes that forms by a novel developmental process.". PLoS Biology. doi:10.1371/journal.pbio.1001912. PMID 25051267. 
  5. ^ Johnson MC, Kamm RD. "The role of Schlemm's canal in aqueous outflow from the human eye." Invest Ophthalmol Vis Sci. 1983 Mar;24(3):320-5. PMID 6832907.
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