The Anterior Chamber

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OPTOMETRY · SEMESTER 2

The Anterior Chamber

Ocular Anatomy and Physiology

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The Anterior Chamber

CHAPTER 8.

THE ANTERIOR CHAMBER

BY THE END OF THIS CHAPTER YOU WILL HAVE COVERED THE

FOLLOWING ASPECTS OF THE TOPIC

  • 1. DEFINITON, BOUNDARIES, DIMENSIONS
  • 2. THE ANTERIOR CHAMBER ANGLE
  • 3. THE POSTERIOR CHAMBER
  • 4. THE AQUEOUS HUMOUR COMPOSITION AND DYNAMICS
  • 5. CLINICAL CONSIDERATIONS
  • 1. DEFINITION , BOUNDARIES , DIMENSIONS.

The anterior chamber (AC ), is the space between the cornea ,lens and iris.

It is bounded anteriorly be the corneal endothelium , posteriorly by the anterior capsule of the lens and iris.

  • The anterior and posterior boundaries meet laterally, to form the anterior chamber angle.

A sieve-like, porous structure called trabecular meshwork is seen at the angle.

The anterior chamber is filled with an optically clear, transparent fluid called the aqueous STS humour leaves the anterior chamber by passing through the The volume of the AC varies, but averages 0.2mls.

  • The errr of the anterior chamber varies too, depending upon age, sex and
  • It is 3mm deep at its center, becoming shallower towards the periphery
  • (angle).
  • Chamber depth decreases with age at an approximately 0.01mm per year .
  • It is shallowefiinifémaléstandilinuhyperopiay deeper in males and in myopia.
  • 2. THE ANTERIOR CHAMBER ANGLE.
  • This is the angle
  • The normal angle width is roughly 40°.
  • The a width tends to be grectest in Caucasians, less in black Africans
  • 47
  • The angle can be visualised clinically with the aid of a special mirror called
  • the gonioscope and the procedure ts called gonioscopy.
  • Four anatomical structures can be identified gonioscopically at the angle:
  • a. Schwalbe’s line: represents the peripheral termination of the inner
  • layer of the corneai.e. the point where the endothelial cell layer merges
  • with the sclera.
  • b. Trabecular meshwork : this is the sieve like structure mentioned
  • above through which aqueous humour leaves the anterior chamber.
  • c. Scleral spur: is a spike like ridge of scleral tissue that projects
  • internally into the anterior chamber.
  • d. Ciliary body:
  • , especially in eyes that high axial length as in
  • monn or in eam who had undergone cataract extractions
  • Schwalbe's line
  • Trabecular meshwork
  • |
  • I
  • |
  • i
  • }
  • 1
  • Scleral spur | s
  • | Le
  • Iris processes ! ep) rs ail
  • Fig. 8.1. Diagram representing the anatomical structures on the
  • anterior chamber angle.
  • 48
  • The trabecular
  • Some of the fibres of the ciliary body are attached to the scleral spur
  • posteriorly too.
  • @ Edit with WPS Office
  • This arrangement makes the scleral spur to be a “ connector ” between
  • the ciliary body and the trabecular meshwork.
  • When the ciliary body muscles contract, specifically the transverse
  • muscles, it exerts a pull on the scleral spur, which in turn pulls the
  • trabecular meshwork thus opening its pores.
  • This is thought to be one of the ways through which aqueous flows out
  • of the anterior chamber.
  • 3. THE POSTERIOR CHAMBER:
  • fg The contents of the posterior chamber are:
  • a. The crystalline lens
  • b. Suspensory ligaments of the lens
  • c. Major part of the ciliary body
  • d. Vitreous base
  • Into the posterior chamber is secreted the aqueous humour produced by
  • the ciliary body.
  • The anterior and peso a chambers i
  • 4. THE AQUEOUS HUMOUR COMPOSITION AND DYNAMICS.
  • The aqueous humour is the transparent fluid that fills the anterior and
  • posterior chambers .
  • Fe a ae ror bloo Plssmaiheniiseereted by Ahseiiaryepihiciim
  • The fluid passes through the pupil into the anterior chamber; circulates in
  • the anterior chamber, providing oxygen and nutrients for the lens and
  • corneal endothelium then slowly drains mostly through the trabecular
  • meshwork.
  • 49
  • 4.1. Aqueous humour formation and functions.
  • Aqueous humour is produced from blood plasma ifithelciliaryiprocessesl)
  • Enters the posterior chamber from the ciliary processes by means of :
  • e diffusion;
  • e ultrafiltration;
  • e active secretion.
  • The active secretion or transport
  • The rate of aqueous formation in humans is about 2u!/min .
  • Aqueous formation has diurnal fluctuations the highest rate being usually
  • It decreases during the day to reach a 50% decrease during sleep.
  • The constant flow of aqueous helps:
  • e to maintain an adequate intraocular pressure (IOP), values between 10
  • -21mmHg being necessary for the structural integrity and normal
  • functioning of the eye.
  • to supply nutrients to the anterior segment tissues;
  • to carry away metabolic wastes;
  • to facilitate immune responses ;
  • to serve as an antioxidant.
  • 4.2. Aqueous humour composition.
  • The protein level is low , markedly lower than the plasma levels.
  • This is explained by the presence of blood- aqueous barrier , which blocks
  • the passage of large molecules while still allowing a flux of ions and low
  • molecular weight solutes.
  • The essentially protein-free status of the aqueous explains its optical
  • clarity.
  • Other components include:
  • glucose,
  • oxygen,
  • ascorbate,
  • glutathione,
  • enzymes,
  • growth factotrs,
  • ions, electrolytes,
  • carbon dioxide, lactate.
  • 50
  • 4.3. Aqueous humour outflow occurs by two mechanisms :
  • e trabecular (pressure dependent ) outflow;
  • e uveoscleral ( pressure independent ) outflow.
  • |
  • a. The trabecular ( pressure dependent ) outflow.
  • Most of the aqueous is drained by this mechanism.
  • The trabecular meshwork
  • It functions
  • From the trabecular meshwork the fluid ent erSisehlémmsicanaland
  • drains into the episcleral veins.
  • Decreased trabecular outflow is a characteristic of glaucoma and elevated
  • b. The uveoscleral ( pressure independent ) outflow occurs across the
  • Drains about 10% of the aqueous.
  • ro account for a greater than normal percentage of outflow in
  • It is increased by eycloplegics and decreased by miotics.
  • 51
  • Fig. 8.2. Diagram of the anterior chamber angle and the flow of
  • aqueous.
  • 5. CLINICAL CONSIDERATIONS.
  • The balance between the aqueous production and outflow maintains the
  • intraocular pressure (IOP) and it is extremely important to the proper
  • functioning of the eye.
  • Decreased outflow facilities and elevated intraocular pressure is
  • characteristic of a disease called glaucoma.
  • An increased rate of aqueous formation is rarely, if ever, the cause of raised
  • IOP.
  • Blood in the anterior chamber is called hyphaema.
  • Pus in the AC is called hypopion.
  • Abnormal vessels growing in the AC angle are known as angle
  • neovascularisation.
  • A thickened Schwalbe’s line is known as posterior embryotoxon.

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