Chapter 9: Aqueous humor, Iris, and Ciliary Body

Question 1

What is the function of the aqueous humor?

Answer 1

• provides nutrients to support the Anterior segment tissues
• removes metabolic waste products
• helps maintain appropriate IOP

Question 2

Where is the aqueous humor produced? What is the flow rate?

Answer 2

It is secreted by the non-pigmented epithelium of the ciliary body from a substrate of blood plasma

Flow rate= 2-3 micro Liters per minute

Question 3

How does the aqueous humor enter the posterior chamber from the ciliary body?

Answer 3

It enters via both active and passive mechanisms
Active= Carbonic Anhydrase II activity
Passive= diffusion and ultrafiltration

Question 4

Which layer of the ciliary body has tight junctions? Which has leaky junctions?

Answer 4

The NPE of the ciliary body has tight junctions proximal to the apical plasma membrane, and helps to establish the blood-aqueous barrier
The PE is leaky, and allows solutes through intercellular spaces

Question 5

How do Carbonic anhydrase inhibitors and beta blockers used to treat glaucoma?

Answer 5

they both decrease the rate of aqueous humor formation in the NPE of the ciliary body

Question 6

Describe the process of aqueous formation by the ciliary body

Answer 6

1- solutes/h2O are taking in by the PE at their stromal surface
2- Transferred to NPE via gap junctions
3- Transferred from NPE into the posterior chamber

Question 7

What are the components of the aqueous humor? What are the major Anions?

Answer 7

• Inorganic Ions - Organic anions - carbohydrates
• glutathione - urea - proteins
• growth modulatory factors - 02/CO2

Major anions= HCO3, CL

Question 8

How do the ionic concentrations in the aqueous humor compare to serum?

Answer 8

NaK/Mg/Fe/Cu/Zn are similar to plasma concentrations

Ca+2 is 50% of plasma level

Question 9

What organic anions are found in the aqueous humor?

Answer 9

Lactate (aqueous>plasma)
vitamin C (ascorbic acid)

Question 10

How does the glucose level of the aqueous compare to serum?

Answer 10

The aqueous has 70% of the glucose found in the serum

However, inosital is 10x greater than the serum levels, due to its importance for phospholipid synthesis ion the anterior segment

Question 11

WHat is the function of glutathione in the aqueous humor?

Answer 11

It stabilizes the redox state of the aqueous by re-converting ascorbate to its functional form after oxidation, and removal of excess H202

Therefore, protects tissues from oxidative damage.

Is highly concentrated in the ocular ciliary epithelium

Question 12

What is the urea concentration of the aqueous compared to plasma?

Answer 12

Its concentration is 80-90% of its plasma value

Question 13

What is the protein concentration of the aqueous humor? What are the most abundant proteins found in the aqueous himor?

Answer 13

0.02 g of protein per 100 mL

Albumin and Transferrin are the most abundant proteins, accounting for 50% of total protein

Question 14

What are the proteinases/inhibitors found in the aqueous humor?

Answer 14

Cathepsin D and O, which are synthesized in the ciliary epithelial cells.
Cathepsin D is involved in the degradation of neuropeptides and peptide hormones.
Cathepsin O function is unknown

Question 15

How do the levels of growth modulatory factors in the aqueous change in patients with DM?

Answer 15

Levels of Insulin-Like growth Factor binding proteins (IGFBP) are 5x higher in patients without retinopathy

IGF-1 is increased in patients with diabetic retinopathy

Question 16

What VEGFs are found in the aqueous humor? What is the significance of VEGF-A?

Answer 16

VEGF A-D, adn placental Growth factor are found in the aqueous.

VEGF A is the only member of its family induced by hypoxia–it is a crucial regulator of angiogenesis and a potent inducer of vascular permeability.

Levels of VEGF A increase in patients with active neovascularization from PDR, CRVO, and NVI

Question 17

What are the partial pressures of 02 and CO2 in the aqueous humor? Where is the 02 in the aqueous derived from? What is the pH of the aqueous humor?

Answer 17

O2- 55 mm Hg CO2- 40-60 mm Hg
02 is derived from blood supply to ciliary body
pH= 7.5-7.6

Question 18

How does the protein content of the aqueous humor change s/p blood-aqueous barrier breakdown? What consequences would it have?

Answer 18

There would be a 10-100x increase in protein

Could cause formation of fibrinous exudates, clot formation (with or without macrophage reaction and formation of cyclitic membrane), and synechiae formation (peripheral and posterior)

Question 19

Chronic disruption of the blood-aqueous barrier has been implicated in several intraocular processes–what are they?

Answer 19

abnormal hypoplastic response of the lens epithelium, corneal endothelium, TM, Iris, and formation of complicated cataracts.

Question 20

What embryologic tissues are the Iris and CB derived from?

Answer 20

They are both derived from Neuroectoderm

Question 21

How does PGF2 agonists work to treat glaucoma?

Answer 21

Unlike BB’s/CAIs/Alpha 2 agonists, PGF2 decrease IOP by increasing outflow.

Typically lowers IOP by 27-35%

Question 22

What effect do Arachidonic Acid/PGE/PGF have on the eye when administered topically or intracamerally?

Answer 22

When administered intracamerally or topically at high concentrations, they cause miosis, increased IOP, increased aqueous protein content, and entry of WBS into the tear fluid and aqueous.

Question 23

What are the functions of PGs?

Answer 23

Exert effects by interacting with G coupled 7 transmembrane receptors

• regulation of smooht muscle contractility
• mediation of pain and fever
• regulation of BP and PLT aggregation
• other physiologic defense mechanisms( immune and inflammatory responses)