Anatomy of Anterior Chamber by Dr. Parthopratim Dutta Majumder

Anterior chamber is an angular space bounded anteriorly by the posterior (inner) surface of the cornea and posteriorly by the anterior surface of the iris and a part of cilliary body.

Boundary of anterior chamber:

Anteriorly

Posteriorly

  1. Inner surface of the cornea
  2. At periphery, trabecular meshwork
  1. Lens,
  2. Anterior surface of the iris and
  3. Anterior face of the ciliary body.

 

Anterior chamber is 3 mm deep and it contains 0.25 ml of the aqueous humour. Anterior chamber depth is shallower in the hypermetropic eye than the myopic eye. It is also shallower in children and in older people.

Anterior Chamber at a glance

  1. Volume: 220 µL.
  2. Chamber Volume decreases by 0.11 µL/year life
  3. Depth: 3.15mm (2.6- 4.4mm)
  4. Chamber depth decreases by 0.01mm/year of life.
  5. Chamber depth is shallower in the hypermetropic than myopic .Chamber deepens by 0.06mm for each diopter of myopia.
  6. Chamber depth is slightly diminished during accommodation, partly by increased lens curvature & partly by forward translocation of the Lens.
  7. Wide angle of anterior chamber denotes the eye in which the angle between iris and surface of the trabecular meshwork is between 20 to 45 degrees.  Angles less than 20 degrees are termed as narrow angles.( Becker- Shaffer's diagnosis and therapy of glaucomas)

Parts of anterior chamber:

Scleral sulcus and scleral spur:
Limbus is the transition zone between the cornea & sclera. On the inner surface of the limbus, there is an indentation or groove, which is known as the scleral sulcus.

This scleral sulcus has a sharp posterior margin- the scleral spur & a sloping anterior wall which extends to the peripheral cornea.The ciliary body is attached to the scleral spur and there exists a potential space, the supraciliary space, between ciliary body and the sclera. Iris inserts into the anterior side of the ciliary body and the part of the ciliary body between root of iris & scleral spur is known as ciliary band.

Scleral spur is composed of a group of fibres known as scleral roll. Scleral roll is composed of 75-80% collagen + 5% elastic tissue. This circular structure prevents ciliary muscle from causing Schlemm’s canal to collapse.

Canal of Schlemm:
A sieve or net like structure, the trabecular meshwork, bridges the scleral sulcus converting it into a tube, which is known as schlemm’s canal. It is a circular canal with a diameter of 190 to 350 microns, in the sclera which lies posterior to the sclerocorneal junction.as mentioned, it can be compared with a tube situated in side the sclera surrounding limbus. Though rarely there can be a plexus rather than a discrete canal.  It is also called sinus venous sclerae. On cross section it is oval in shape and lined by endothelium. It communicate with anterior chamber  through the trabecular meshwork internally. On the scleral side the canal of Schlemm is perforated by approximately 25 to 30 aqueous collector channels which branch into intrascleral and deep scleral plexi. In conventional route of outflow, aqueous moves into the canal of Schlemm through trabecular meshwork and from their reaches episcleral veins via collector channels that traverse limbal sclera. episcleral veins drain into the ophthalmic veins and thus in general circulations.

 

Schlemm’s canal is named after a German anatomist; Friedrich Schlemm. Interestingly, he was also the first person to describe the corneal nerves.

 

Canal of Schlemm is not a rigid tube and at higher intraocular pressure it often collapses. It can be opened up by a pull on the scleral spur ( exerted by longitudinal ciliary muscle fibres). Cholinergic drugs are used to facilitates the aqueous drainage by opening up the canal based on this mechanism.