Canal of Schlemm

sinus venosus sclerae

The canal of Schlemm is a thin, circular channel running all the way around the eye just outside the trabecular meshwork. It is lined by endothelium, collects aqueous humour that has passed through the meshwork, and empties it through collector channels and aqueous veins into the episcleral veins.

Anatomical Data

Structure & Supply

Location	Circumferentially in the inner sclera at the corneoscleral junction, outside the trabecular meshwork
Parts	Inner wall endothelium Outer wall Collector channels Aqueous veins
Nerve Supply	Fibres from the ciliary nerves in surrounding tissue
Blood Supply	Drains into the episcleral and conjunctival veins

Biomechanics

Function & Actions

Collects aqueous humour leaving the trabecular meshwork and returns it to the venous circulation.

Clinical Relevance

Clinical Notes

Because aqueous drains into episcleral veins, anything that raises episcleral venous pressure, such as a carotid-cavernous fistula or Sturge-Weber syndrome, raises eye pressure. Glaucoma procedures such as canaloplasty, goniotomy and stent implants aim to open or bypass flow into the canal. Blood can reflux into the canal and be seen on gonioscopy when venous pressure is high.

Pathology

Common Injuries & Conditions

Congenital Glaucoma

Faulty development of the drainage angle and canal pathway causes raised pressure in infants, with a large cloudy cornea, watering and light sensitivity.

Raised Episcleral Venous Pressure

Increased pressure in the veins receiving Schlemm canal outflow reduces drainage and raises eye pressure, for example with carotid-cavernous fistula.

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