Anterior Chamber

Exam 2

What are the general characteristics of the anterior chamber? Include what is the shape, volume as well as the boundaries of the anterior chamber

• Anterior – posterior surface of cornea

• Posterior –anterior border layer of iris and anterior surface of lens at the pupil

• Lateral – Face of ciliary body, trabecular meshwork and angle structures

• Volume 250 microliters

• Shape: Ellipsoid

• Angle: Where iris and cornea meet

What is the depth and diameter of the anterior chamber?

• Depth: 3.5 to 3.7mm (apex of cornea to lens)

• Diameter: 11.3 to 12.4mm

How does the anterior chamber angle openness vary by age, heredity, refractive error, race and gender?

• Narrows as we age due to thickening of the lens

• Inherit openness of the angle

• Myopes – more open angles

• Hyperopes – more narrow angles

• Asians – more narrow angles

• Blacks – more open angles

• Males – larger than females

What are the major functions of the anterior chamber angle?

• Pathway for aqueous to exit the eye

• Self-cleaning filter – phagocytosis

• Rectifying properties – allows for one-way flow of aqueous out of the angle and into Schlemm’s canal

What are the two major pathways for aqueous to exit the eye? and percentage of outflow

• Conventional pathway – Trabecular meshwork – approx. 80% - highest volume of aqueous outflow

• Uveoscleral Pathway - approx. 20 %

Which pathway accounts for the highest volume of aqueous outflow?

• Conventional pathway – Trabecular meshwork – approx. 80% - highest volume of aqueous outflow

Describe the general ultrastructure of the trabecular meshwork?

• Collagen core – Type I (tensile) Type III (resilience) , elastic fibers surround collagen ( allows for reversible deformation) Core is surrounded by proteoglycans and that is covered by an endothelium

Describe the uveal meshwork and its function.

• Cords of meshwork – 2-3 layers

• Large intertrabecular spaces

• Gross filtration

• Adjacent to anterior chamber

Describe the corneoscleral meshwork and its function.

• Sheets of meshwork with pores – approx. 20 sheets

• Pores get smaller as get closer to Schlemm’s canal – pores run through endothelial cells that line the meshwork

Describe the Anterior Trabecular Meshwork.

Most anterior portion of meshwork – considered non-filtering portion of meshwork

Discuss the composition and location of Schwalbe’s Line including

• Most anterior structure of the angle – transition between TM and endothelium of cornea

• (Descemet’s membrane ends)

• Circumferential ring of collagen and elastin.

• Pigmented Schwalbe’s line – Sampaolesi’s line – pigmented Schwalbe’s line

• Thickened and anteriorly displaced Schwalbe’s line – Posterior Embryotoxon

Describe the composition and location of the Scleral spur.

• Circumferential scleral fibers that are adjacent to Schlemm’s canal – histology is similar to sclera stroma except contains a few more elastin fibers. TM attaches to the spur and CB fibers attach to the spur

How does the corneal endothelium compare to the trabecular meshwork endothelium?

• Both are metabolically active

• Neither exhibit mitosis under normal conditions – TM may have limited mitosis after laser tx

• Both increase in size with age

• Both decrease in number with age

• Different functions

How does trabecular meshwork carry out its function as a self-cleaning filter?

Engulfs and ingests debris from TM - Phagocytosis

What are the “smooth muscle” properties of the trabecular meshwork endothelial cells and how could these properties be used to lower intraocular pressure?

• TM endothelial cells possess large number of transporters, channels and receptors which are known to regulate smooth muscle. Also have contractile like properties.

• RhoKinase inhibitors relax TM endothelial cells to relax and open the meshwork to lower IOP – one mechanism. RhoKinase inhibitors also enhance episcleral outflow.

What is the composition of the juxtacanalicular tissue(JCT) and how does this slow the flow of aqueous?

• Collagen fibers and high concentration of GAGS – very viscous environment slows flow of aqueous

• The JCT offers the greatest resistance to the outflow of aqueous

What is the function of the juxtacanalicular cells?

• Produce extracellular substances (GAGS. Also send out cytoplasmic processes to attach to inner wall of Schlemm’s canal as well as to corneoscleral TM. This prevents separation of Schlemm’s canal from TM during changes in IOP.

What is the juxtacanalicular tissue/cribriform plexus and how does contraction of the ciliary body affect the juxtacanalicular tissue, aqueous outflow and intraocular pressure?

The cribriform plexus consists of elastic like fibers that connect the juxtacanalicular tissue and

the inner wall of Schlemm’s canal to the longitudinal muscle fibers of ciliary body. With

contraction of the ciliary muscle, the outflow of aqueous is enhanced through the JCT and the

inner wall of Schlemm’s canal. This helps to lower IOP

What is the size and location of Schlemm’s canal?

• Schlemm’s canal is oval shaped lymphoid like sinus that runs 360 degrees in the internal scleral sulcus. It has a circumference of 36mm.

What are the characteristics of the inner wall of Schlemm’s canal and how does this affect

aqueous outflow?

• The ultrastructure of the endothelial cells has discontinuous zonula occludens. Some aqueous flows via pinocytosis. This creates a pressure on the inner wall of the canal and slows down the flow of aqueous outflow.

How does most of aqueous enter Schlemm’s canal via the inner wall? How do the giant vacuoles prevent the regurgitation of aqueous back into Schlemm’s canal?

• The endothelial cells that line the inner wall of Schlemm’s canal in response to increase pressure, form giant vacuoles. The vacuoles open up on the lumen side of the canal to release the aqueous in a one-way direction to prevent regurgitation of aqueous back into the trabecular meshwork. The higher the pressure, the more vacuoles that form to move more aqueous into Schlemm’s canal. Therefore, it is a pressure dependent system. inner wall of Schlemm’s canal produces giant vacuoles

What is the function of Sondermann’s, afferent or internal collector channels?

• These are outpouchings of the inner of Schlemm’s canal that function to increase surface area-for more giant vacuole formation.

Where do the external or efferent collector channels connect to and where do they ultimately drain?

These are channels that exit via the outer wall of Schlemm’s canal. They drain into aqueous veins or into several venous plexi which drain into episcleral veins that ultimately drain into ophthalmic veins.

How do we get blood from episcleral veins into Schlemm’s canal? Why does this blood not enter the anterior chamber aqueous?

Because there is a direct connection between the venous system and Schlemm’s canal, pressure on the venous system can cause regurgitation of blood back into the canal. If this occurs short term, it is usually not a clinical problem. (ie excessive pressure via a three mirror gonio lens) Long term blood in Schlemm’s canal can cause secondary glaucoma. Blood does not enter the anterior chamber because of the zonula occludens of the inner wall of Schlemm’s canal and because of the one-way system of aqueous outflow (giant vacuoles).

Describe the flow of aqueous through the uveoscleral pathway

• Aqueous enters face of ciliary body or anterior border layer of iris -> between ciliary muscle fibers-> supraciliary space - > vortex veins