Lecture 10 - Anterior Chamber

Ocular Anatomy

What is the shape of the anterior chamber (AC)?

The anterior chamber is elliptical in shape.

What is the depth of the anterior chamber?

The depth of the anterior chamber is 3–4 mm.

What is the diameter of the anterior chamber?

The diameter of the anterior chamber is 11–12 mm.

What is the volume of the anterior chamber?

The volume of the anterior chamber is approximately 250 µL.

What are the factors that impact anterior chamber depth?

Factors include age, refractive error, and race.

How does age affect anterior chamber depth?

Anterior chamber depth decreases with age.

How does refractive error affect anterior chamber depth?

Myopes tend to have a larger anterior chamber compared to hyperopes.

How does race affect anterior chamber depth?

Asians typically have a narrower anterior chamber than other races.

What forms the anterior boundary of the anterior chamber?

The corneal endothelium forms the anterior boundary.

What forms the peripheral boundary of the anterior chamber?

The trabecular meshwork, portion of ciliary body, and iris root form the peripheral boundary.

What forms the posterior boundary of the anterior chamber?

The anterior iris surface and pupillary area of the anterior lens form the posterior boundary.

Where is the anterior chamber angle located?

It is located at the periphery of the anterior chamber, where the corneoscleral tissue and iris meet.

What fluid fills the anterior chamber?

The anterior chamber is filled with aqueous humor.

What does aqueous humor provide nutrients to?

It provides nutrients to the cornea, lens, and trabecular meshwork.

Where does aqueous humor exit the eye?

It exits the eye at the anterior chamber angle.

What is the direction of aqueous flow?

The direction of flow is always outward.

What are the structures of the anterior chamber angle from posterior to anterior?

Iris surface, ciliary body, scleral spur, trabecular meshwork, Schwalbe’s line.

“I Can See This Line”

What is gonioscopy used for?

Gonioscopy is used to view the anterior chamber angle.

How does gonioscopy work?

It uses mirrors to direct light into the anterior chamber angle, allowing visualization.

What does the view in gonioscopy simulate?

It is as if the observer is standing on the lens and looking across the iris into the anterior chamber angle.

What is Schwalbe’s line?

It is the most anterior structure in the anterior chamber angle.

What is Schwalbe’s line composed of?

It is a ring of collagen and elastin.

What does Schwalbe’s line mark anatomically?

It marks the termination of Descemet’s membrane and the outer limit of the cornea.

What transition does Schwalbe’s line represent?

It represents the transition between corneal endothelium and trabecular meshwork.

How does Schwalbe’s line appear during gonioscopy?

It appears as a shiny white line.

What is a Sampaolesi’s line?

It is an accumulation of pigment along Schwalbe’s line, often due to disease or trauma.

What is a posterior embryotoxin?

It is an anteriorly displaced Schwalbe’s line.

Is the trabecular meshwork vascular or avascular?

It is avascular.

How does the trabecular meshwork encircle the eye?

It encircles the anterior chamber circumferentially.

What is the shape of the trabecular meshwork in cross-section?

It is triangular in shape.

Where is the apex of the trabecular meshwork located?

The apex is at Schwalbe’s line.

Where is the base of the trabecular meshwork located?

The base is at the scleral spur and ciliary body.

What does the inner face of the trabecular meshwork border?

It borders the anterior chamber.

What does the outer side of the trabecular meshwork lie against?

It lies against the cornea, sclera, and Schlemm’s canal.

How is the trabecular meshwork structured?

It is made of flat, perforated sheets.

How many sheets are there near the apex of the trabecular meshwork?

There are 3–5 sheets near the apex.

How many sheets are there near the base of the trabecular meshwork?

15–20 sheets as they extend posteriorly.

What connects the spaces between trabecular sheets?

The spaces are connected through pores.

How does the pore size change as aqueous approaches Schlemm’s canal?

Pores become smaller near Schlemm’s canal.

Does the trabecular meshwork have direct apertures to Schlemm’s canal?

No, it does not have direct apertures.

What are the three divisions of the trabecular meshwork?

Uveal meshwork, corneoscleral meshwork, and juxtacanalicular tissue (JXT).

What is the uveal meshwork?

It is the inner region adjacent to the anterior chamber with 2–3 sheets and large pores for gross filtration.

What is the corneoscleral meshwork?

It is the middle region with 15–20 sheets containing smaller pores for fine filtration.

What is the juxtacanalicular tissue (JXT)?

It is the outermost region, between the corneoscleral meshwork and Schlemm’s canal, with very fine pores for ultrafine filtration.

What does the JXT separate?

It separates the basement membrane of Schlemm’s endothelial cells from the trabecular meshwork.

What is the composition of JXT?

It consists of endothelial cells, fibroblasts, collagen, elastic fibrils, and ground substance.

What do JXT cells connect to?

They form connections with the endothelium of Schlemm’s canal.

What do elastic fibrils of JXT anchor to?

They anchor to Schlemm’s canal endothelial cells, scleral spur, and ciliary muscle tendons.

How does ciliary muscle contraction affect Schlemm’s canal?

It opens Schlemm’s canal by pulling on the elastic fibrils.

What are trabecular beams (trabeculae) made of?

They are composed of collagen fibers and elastin, covered by basement membrane and TM endothelial cells.

What is the function of trabecular beams?

They provide structural support and form a mesh-like network.

What is the role of extracellular matrix in the TM?

It contains glycosaminoglycans (GAGs) that bind water to form a gel aiding in filtration.

What regulates resistance to aqueous outflow in TM?

Matrix metalloproteinases (MMPs) modulate the extracellular matrix composition and arrangement.

What are the functions of TM endothelial cells?

They maintain TM function, phagocytose debris, secrete GAGs, and participate in tissue repair.

What organelles do TM endothelial cells contain for debris clearance?

Phagosomes and lysosomes.

What cytoskeletal structures do TM endothelial cells contain?

Actin filaments and microtubules for structural remodeling in response to pressure changes.

What types of junctions exist in TM endothelial cells?

Gap and tight junctions for communication and barrier function.

During gonioscopy, how does the trabecular meshwork appear?

It appears as two divisions: anterior TM and posterior TM.

What characterizes the anterior TM?

It lies anterior to Schlemm’s canal and shows minimal or no pigmentation.

What characterizes the posterior TM?

It drains into Schlemm’s canal and is often pigmented.

What is Schlemm’s canal?

It is a circular venous channel lined by endothelial cells.

What does Schlemm’s canal normally contain?

It normally contains aqueous humor, not blood.

What percentage of aqueous drainage occurs through Schlemm’s canal?

It is responsible for up to 90% of aqueous outflow.

Is Schlemm’s canal normally visible in gonioscopy?

No, unless it is filled with blood.

What are the two endothelial walls of Schlemm’s canal?

The inner wall (facing anterior chamber) and outer wall (facing sclera).

What does the inner endothelial wall of Schlemm’s canal lie against?

It lies against the scleral spur and trabecular meshwork.

What special structures does the inner wall contain?

Tight junctions, internal collector channels, and giant vacuoles with pores.

What is the function of internal collector channels?

They are evaginations that extend into JXT to increase surface area for aqueous transport.

What does the outer endothelial wall of Schlemm’s canal lie against?

It lies against the sclera near the limbus.

What are the two drainage pathways from Schlemm’s canal to venous system?

External collector channels (main) and aqueous veins (secondary).

Describe the external collector channel pathway.

Schlemm’s → external collector channels → deep scleral plexus → intrascleral plexus → episcleral veins → vortex veins → ophthalmic veins → cavernous sinus.

Where do aqueous veins drain?

Directly into episcleral veins → vortex veins → ophthalmic veins → cavernous sinus.

What is the scleral spur?

It is a circular band of collagen and elastin fibers that extends from the sclera.

What structures attach to the scleral spur?

Ciliary muscle fibers and trabecular meshwork fibers.

What happens to the scleral spur during accommodation?

The ciliary body contracts, pulling the spur, which opens the trabecular meshwork to increase drainage.

Is the ciliary body visible during gonioscopy?

Yes, it is visible.

What are the two mechanisms by which the ciliary body increases aqueous drainage?

1. Longitudinal muscle attachment to scleral spur and TM, pulling open TM during contraction.

2. Longitudinal muscle attachment to JXT and Schlemm’s inner wall, pulling them to increase drainage.

What is another name for aqueous humor?

Aqueous

What is the function of aqueous humor?

It sustains the cornea, lens, and trabecular meshwork, and removes metabolic waste.

Where is aqueous humor produced?

It is produced by the pars plicata of the ciliary body.

What is the rate of aqueous humor production?

2–3 µL per minute.

Describe the pathway of aqueous flow.

It is secreted into the posterior chamber, passes between iris and lens, enters the anterior chamber via the pupil, and drains at the angle.

What are the three processes of aqueous formation?

Diffusion, ultrafiltration, and active secretion.

Which process of aqueous formation is the main mechanism?

Active secretion.

What is the osmotic nature of aqueous humor?

It is isotonic with ~98% water content.

What affects the viscosity of aqueous humor?

Protein content—higher protein increases viscosity.

What is the relationship between viscosity and outflow resistance?

Increased viscosity leads to increased resistance to outflow.

How do thermal convection currents affect aqueous flow?

The cooler cornea and warmer iris cause aqueous near iris to rise, cool near cornea, and sink back down.

What are the two aqueous outflow mechanisms?

Trabecular (conventional) and uveoscleral (unconventional) outflow.

What percentage of aqueous exits via the trabecular outflow?

Approximately 85%.

Describe the trabecular (conventional) outflow pathway.

TM → Schlemm’s canal → external collector channels → venous system.

Is trabecular outflow pressure-dependent?

Yes, it depends on IOP and TM resistance.

Does trabecular outflow increase with IOP?

Trabecular outflow increases with IOP until it reaches a high pressure, then Schlemm’s canal collapses and outflow decreases.

What percentage of aqueous exits via the uveoscleral outflow?

Approximately 15%.

Describe the uveoscleral (unconventional) outflow pathway.

Ciliary muscle → supraciliary space → suprachoroidal space → venous circulation of sclera and choroid.

Is uveoscleral outflow pressure-dependent?

No, it is constant and not pressure-dependent.

What happens when there is increased resistance to aqueous outflow?

Intraocular pressure increases.

What can increase resistance in the trabecular meshwork?

Pigment or debris accumulation, loss of TM cells, or adhesions between TM fibers.

How can Schlemm’s canal contribute to increased IOP?

Narrowing or collapse of Schlemm’s canal increases IOP.

What is the only treatment goal in glaucoma?

Reduction of intraocular pressure.