Drainage of the Aqueous Humor

Question 1

What force generates the IOP?

Answer 1

The pressure that the aqueous humor exerts on the internal surface area of the anterior eye.

Question 2

IOP is measured in what?

what is the average measurement?

Answer 2

Measured in mmHg.
Range is 10-21.
Average is 15.5

Question 3

Aqueous drains out of the anterior angle through

Answer 3

The anterior chamber angle AKA the iridocorneal angle or angle

Question 4

The iridocorneal angle is formed by the

Answer 4

Iris and the cornea

Question 5

6 structures that are in the iridocorneal angle

Answer 5

1. Iris root.
2. Anterior border of the ciliary body.
3. Scleral spur
4. Trabecular meshwork
5. Schlemm’s canal
6. Schwalbe’s line

Question 6

How does the iris root contribute to the angle

Answer 6

Peripheral region of the iris that is continuous with the ciliary body is the iris root.
With the cornea, it forms the iridocorneal angle

Question 7

What is the iris root

Answer 7

Peripheral region of the iris that is continuous with the ciliary body

Question 8

Where is the anterior border of the ciliary body

Answer 8

Region of the ciliary body near the iris root.

Question 9

Scleral spur’s anterior border is continuous with _____ and is anchored into ____.
_____ fibers attach to the posterior border

Answer 9

Collagen of the trabecular meshwork and is anchored into schlemm’s canal.
Longitudinal ciliary muscle fibers attach to the posterior border.

Question 10

Trabecular meshwork contains what

Answer 10

It is a meshwork of connective tissue (collagen, ground substance, elastin) and instead of fibroblasts, it has endothelial cells that come from the cornea.

Question 11

The endothelial layer of the cornea becomes what at the limbus?

Answer 11

Becomes the endothelial cells of the trabecular meshwork

Question 12

What is the role of endothelial cells in the trabecular meshwork?

Answer 12

1. They produce the connective tissue components
2. They phagocytize debris in the aqueous as it drains through the trabecular meshwork.
3. They contain numerous aquaporins in the cell membrane.

Question 13

Are there more layers of meshwork posteriorly or anteriorly?

Answer 13

More layers posteriorly (15-20) than anteriorly (3-5)

Question 14

Is the posterior meshwork is pigmented or nonpigmented?

Is the anterior layer is pigmented or non pigmented?

Answer 14

Posterior- pimented

Anterior- non pigmented

Question 15

Posterior meshwork is juxtaposed to ____ and the anterior meshwork is juxtaposed to ___

Answer 15

Juxtaposed to Schlemm’s canal

Juxtaposed to limbal stroma

Question 16

Regions of the trabecular meshwork inner to outer

Answer 16

Inner
Uveal meshwork
Corneoscleral meshwork
Juxtacanalicular meshwork

Question 17

Uveal meshwork (inner)

1. Connective tissue is __-like with ___ pores.
2. Located in which areas of the trabecular meshwork- anterior, posterior, or both?
3. Extends from where to where
4. Logitudinal muscle fibers of the ciliary body attach to which border of the uveal meshwork?
5. Contraction of the ciliary muscle ___ the size of the pores

Answer 17

1. Cord like with an endothelial covering and large pores
2. Located in the anterior and posterior trabecular meshwork
3. Extends from schwalbe’s line to the ciliary body
4. Longitudinal muscle fibers of the ciliary body attach to the uveal meshwork’s posterior border
5. Increases the size of the pores

Question 18

Corneoscleral meshwork

1. Connective tissue is __-like and how large are the pores?
2. Where is it located?
3. Extends from where to where?
4. What indirectly occurs when the longitudinal muscle fibers contract?

Answer 18

1. Sheet like and the pores are middle sized compared to the outer and inner layer.
2. It is located in the anterior and posterior trabecular meshwork.
3. It extends from Schwalbe’s line to scleral spur.
4. Contraction of the longitudinal muscle fibers of the ciliary body indirectly increases the size of the pores. This pulls on the scleral spur, which pulls on the corneoscleral meshwork.

Question 19

Juxtacanalicular meshwork (outer)

1. What does this connective tissue look like? how large are the pores?
2. Where is it located?
3. What indirectly occurs when the longitudinal muscle fibers contract?

Answer 19

1. It has endothelial cells enmeshed in it (vs an endothelial covering) with narrow pores.
2. It is located in the posterior trabecular meshwork, juxtaposed to Schlemm’s canal.
3. Contraction of the longitudinal muscle fibers of the ciliary body indirectly increases the size of the pores. This pulls on the scleral spur, which pulls on the juxtacanalicular meshwork.

Question 20

Schlemm’s canal is lined by which cell type

Answer 20

Endothelial

Question 21

What is Schlemm’s canal anchored to by connective tissue?

Answer 21

The Juxtacanalicular meshwork and scleral spur.

Question 22

Endothelial cells near the juxtacanalicular meshwork forms what?

Answer 22

The transcellular channels (giant vacuoles)

Question 23

What is the role of the The transcellular channels (giant vacuoles) in the endothelial cells near the juxtacanalicular meshwork?

Answer 23

Allows aqueous to pass from the juxtacanalicular meshwork into schlemm’s canal.

Question 24

What does Schlemm’s canal drain into?

Answer 24

Drains into 2-8 aqueous veins (of Ascher) and 25-30 intrasceral collector channels.

Aqueous veins drain into episcleral veins.
Intrascleral collector channels drain into the intrascleral venous plexus and then the conj or episcleral veins.

Question 25

Schwalbe’s line is the border of what

Answer 25

Anterior border of the anterior chamber angle.

It is the peripheral termination of Descemet’s membrane

Question 26

How to remember the components of the angle

Answer 26

I can see the line (missing Schlemm’s canal)

• Iris root
• Ciliary body
• Scleral spur
• Trabecular meshwork
• Schwalbes line

Question 27

2 routes that the aqueous can drain out of the anterior chamber

Answer 27

70-90% drain by the Trabecular route.
Anterior chamber - posterior trabecular meshwork - Schlemm’s canal - episcleral vasculature

10-30% drain by the Uveoscleral route.
Anterior chamber - iris root - ciliary body - supraciliaris - suprachoroidal space - vortex veins or absorbed into the scleral stroma.

Question 28

Uveoscleral route.

Answer 28

(10-30% drain this way)
Anterior chamber - iris root - ciliary body - supraciliaris - suprachoroidal space - vortex veins or absorbed into the scleral stroma.

Question 29

Trabecular route.

Answer 29

70-90% drain by the Trabecular route.

Anterior chamber - posterior trabecular meshwork - Schlemm’s canal - episcleral vasculature

Question 30

Factors controlling aqueous drainage

Answer 30

1. Phagocytic properties of endothelial cells in the meshwork
2. Size of pores in the meshwork
3. Number of GAGs. More GAGs hold onto more water.
4. Number of aquaporins. Not enough? IOP increases.
5. Number and size of transcellular channels in the endothelial cells lining Schlemm’s canal.
6. If episcleral venous pressure is higher than IOP, there will be a change or stop in flow since the pressure gradient is disruption. Average is 8-10mmHG
7. Suprachoroidal pressure. (usually 2-4mmHg below the IOP. Must be less in order for aqueous to drain via the uveoscleral route.
8. Prostaglandins. Signal the synthesis of metalloproteinases, which remodel the extracellular matrix. This leads to an increase in drainage through the uveoscleral route as the proteins degrade and remodel the meshwork.
9. Angle size. An open angle allows for ease of aqueous drainage.

Question 31

Normal episcleral venous pressure. What happens if it reaches the same or greater pressure compared to the IOP?

Answer 31

Episcleral venous pressure is 8-10mmHg
IOP is 10-21mmHg.

If the episcleral venous pressure is equal to the IOP, there will be no aqueous flow out of the eye. All fluid will likely stay put since there is no net pressure change.

If the episcleral venous pressure is greater than the IOP, the aqueous/blood within the episcleral veins will be pushed into the eye. The aqueous within the eye will have nowhere to go, and push on the posterior chamber, pushing on the optic nerve.

Likely due to a clot.

Question 32

How do prostaglandins help control aqueous drainage?

Answer 32

Signal the synthesis of metalloproteinases, which remodel the extracellular matrix. This leads to an increase in drainage through the uveoscleral route as the proteins degrade and remodel the meshwork.