Aqueous Humor Dynamics

Question 1

Why do we need aqueous humor?

Answer 1

Provide structure of the globe, nutrition, and refraction of 1.33.

Question 2

What parts of the eye depend on aqueous humor for nutrition? Why?

Answer 2

Cornea and lens. They are both avascular, need nutrition from somewhere.

Question 3

Why does aqueous humor have a constant turnover of fluid in the eye?

Answer 3

There are waste products accumulating in the eye. They need to be removed and replaced with fresh nutrients.

Question 4

What are four things present in the ciliary body?

Answer 4

Muscles, vessels, autonomic nerve terminals, epithelia lining ciliary processes.

Question 5

What three parts does the ciliary body muscle consist of?

Answer 5

Longitudinal, radial, circular.

Question 6

Which part of the ciliary body muscle is the transitional muscle?

Answer 6

Radial.

Question 7

Which part of the ciliary body muscle attaches ciliary body to the limbus?

Answer 7

Longitudinal.

Question 8

Which part of the ciliary body muscle form anterior and inner portions of the ciliary body?

Answer 8

Circular.

Question 9

What is the primary blood supply to the iris and ciliary processes?

Answer 9

Major Arterial Circle located in the ciliary body.

Question 10

How many branches does the MAC supply to the ciliary processes? Which is fenestrated and non-fenestrated?

Answer 10

Two branches.

Posterior:non-fenestrated, anterior:fenestrated.

Question 11

What is the functional unit responsible for the production and secretion of aqueous humor?

Answer 11

Ciliary process.

Question 12

What three things does the ciliary process consist of?

Answer 12

Stroma, capillaries, and epithelium.

Question 13

The two layers of ciliary epithelium surrounding the stroma are?

Answer 13

Pigmented and non-pigmented epithelium.

Question 14

What is the main source of aqueous fluid in the eye?

Answer 14

Blood through carefully controlled filtration processes.

Question 15

Aqueous fluid provides a source of what to the corneal endothelium and lens?

Answer 15

Antioxidants.

Question 16

Why is important that aqueous humor serves as a shock absorber?

Answer 16

If not for aqueous humor, lens would be hitting iris all the time.

Question 17

Why do the lens require antioxidant?

Answer 17

Lens requires antioxidants to remove free radical in order to stop cataracts developing way to faster than we would like.

Question 18

The antioxidant in the aqueous humor we speak of is what?

Answer 18

Vitamin C or ascorbate.

Question 19

Why is calcium removed?

Answer 19

Too much will cause clearly to be decreased and because calcium can cause more cataracts to be generated.

Question 20

Name 4 things removed in aqueous fluid that can potentially cause problems if not removed?

Answer 20

Calcium, cholesterol, hemoglobin, globulin.

Question 21

Other than ascorbate, name one other component that is present in the aqueous fluid?

Answer 21

Bicarbonate.

Question 22

Is it normal to find red blood cells in your aqueous?

Answer 22

No! That’s a problem. Things should not be floating around.

Question 23

What is the true meaning of “secretion”.

Answer 23

Process by which aqueous humor formation is at its maximum.

Question 24

What are three processes by which the ciliary process releases its contents?

Answer 24

Diffusion, ultrafiltration, and secretion (80-90%).

Question 25

During which time is the rate of aqueous humor production largest in a normal individual?

Answer 25

Morning

Question 26

During which time is the rate of aqueous humor production smallest in a normal individual?

Answer 26

Night time.

Question 27

Can glaucoma patients have a different circadian rhythm when it comes to aqueous humor production?

Answer 27

Yes.

Question 28

What two enzymes are responsible for the production of aqueous humor?

Answer 28

Na-K-ATPase and carbonic anhydrase.

Question 29

Is the aqueous humor production an active process or passive process?

Answer 29

Active. Needs energy to work against its concentration gradient.

Question 30

Where is Na-K-ATPase located and what is its function?

Answer 30

Predominantly bound to plasma membrane of non-pigmented epithelium. This enzyme helps push the Na+ ions into posterior chamber to which water follows.

Question 31

Can aqueous humor be altered? As in the amount produced? If so, how?

Answer 31

Yes aqueous humor can be altered depending on the concentration of Na-K-ATPase.

Question 32

What is the purpose of carbonic anhydrase?

Answer 32

Carbonic anhdrase acts on carbonic acid to produce CO2 and H2O.

Question 33

If you stop carbonic anhydrase with an inhibitor, what happens to the production of aqueous humor?

Answer 33

No conversation of carbonic acid to water occurs, so no water produced which causes a decrease production of aqueous humor.

Question 34

What two things are going to help remove aqueous humor from posterior to anterior part of anterior chamber through pupil?

Answer 34

Pressure and anatomical restrictions.

Question 35

What role does the vitreous humor play for the flow of aqueous humor?

Answer 35

Vitreous humor has glycosaminoglycans that allow it to be a gel like substance. This acts as a barrier and pushes aqueous humor to flow through the pupil.

Question 36

How many mechanism are involved in removing aqueous humor from the posterior part of the anterior chamber? What are they?

Answer 36

2. Conventional route via trabecular meshwork | and unconventional route via uveoscleral pathways.

Question 37

If episcleral venous pressure is high, can the fluid still flow out?

Answer 37

Not very well. If IOP is lower than episcleral pressure, fluid cant flow out the eye.

Question 38

What can cause episcleral venous pressure to increase?

Answer 38

Tumor rarely but more commonly, coughing or sleeping.

Question 39

As fluid passes through the plates of trabecular meshwork, how does this fluid get into schlemm's canal?

Answer 39

Vacuoles are formed that take fluid into schlemm's canal.

Question 40

What happens to the aqueous fluid in the uveoscleral pathway?

Answer 40

Fluid passes through connective tissue between ciliary body muscles into suprachoriodal space and out the sclera.

Question 41

What happens to the aqueous fluid in the trabecular pathway?

Answer 41

Fluid passes through trabecular meshwork, into schlemm's canal to collector channels, and out to the episceral venous circulation.

Question 42

What can cause increase in the spaces between muscles?

Answer 42

Medications we give that increases these spaces between muscle by restructuring features and allowing more fluid to go out.

Question 43

True or False: We can measure the uveoscleral outflow.

Answer 43

False. Total outflow-trabecular outflow=uveoscleral outflow.

Question 44

What is the percentage of trabecular outflow?

Answer 44

70-95%.

Question 45

What is the percentage of uveoscleral outflow?

Answer 45

5-30%.

Question 46

Both total and trabecular outflow decline with what?

Answer 46

Age. As we grow older, we are not able to remove fluid from the eye so well.

Question 47

What two things are joined together by tight junctions that allow for a blood aqueous barrier to be present?

Answer 47

RPE and non-pigmented epithelium of the ciliary processes.

Question 48

What other two things in the eye have a blood-aqueous barrier?

Answer 48

Schlemm's canal endothelium and the capillaries of the iris and retina are non-fenestrated.

Question 49

Internal ocular pressure if the outcome of what two factors?

Answer 49

Inflow and outflow.

Question 50

If plasma components increase in anterior chamber due to a breakdown of blood aqueous barrier (proteins get released with the aqueous humor), should IOP increase?

Answer 50

Yes.

Question 51

During diseases, trauma, or drug induced breakdown of the blood aqueous barrier, what helps the IOP to decrease?

Answer 51

Pseudofacility.

Question 52

What is pseudofacility?

Answer 52

Aqueous inflow via ultrafiltration is suppressed, slowing down the rise of IOP.

Question 53

Can glaucoma exist without a high IOP?

Answer 53

Yes.

Question 54

Normal range of IOP is?

Answer 54

Mean IOP 15.8 SD 2.57, magic number 21. (Not actually mean this much though, keep in mine).

Question 55

What are some factors that affect IOP?

Answer 55

Inheritance, age, gender, refractive error.

Question 56

What is the maximum contributor factor to IOP?

Answer 56

Inheritance.

Question 57

As an individual gets older, what happens to IOP?

Answer 57

Increases because aqueous outflow is decreased with age.

Question 58

Do females or males have higher IOP after the age of 40?

Answer 58

Females have increase in IOP after the age of 40.

Question 59

Do myopic or hyperopic patients have higher IOP?

Answer 59

Hyperopic because smaller eyeball causes greater pressure.

Question 60

During winter, does IOP increase or decrease?

Answer 60

Increase because venous flow is obstructed with gain weight.

Question 61

Moving eyes left to right, like saccades does what to the IOP?

Answer 61

Increase.

Question 62

Appropriate exercise increase or decrease IOP?

Answer 62

Decrease.

Question 63

Supine position increase or decrease IOP?

Answer 63

Increase.

Question 64

Blinking or forcefully closing eye increase or decrease IOP?

Answer 64

Increase.

Question 65

Exhaling with your mouth closed cause IOP to increase or decrease?

Answer 65

Increase.

Question 66

Eye movement cause increase or decrease in IOP?

Answer 66

Increase.

Question 67

Does alcohol cause an increase or decrease in IOP?

Answer 67

Decrease. It's a de-hydrant that moves water from all cells in the body, including the eye.

Question 68

Does a lot of water cause increase or decrease in IOP?

Answer 68

Increase.

Question 69

Does caffeine cause increase or decrease in IOP?

Answer 69

Increase.

Question 70

Does tobacco cause increase or decrease in IOP?

Answer 70

Increase. Especially in new smokers. (Increase BP and pulse rate to increase and causes more fluid to flow into eye and constriction so essentially increases IOP).

Question 71

Does heroin and marijuana cause an increase or decrease in IOP?

Answer 71

Decrease. Not enough for therapeutic level.

Question 72

The current standard tonometry to measure IOP is called what?

Answer 72

Goldmann.

Question 73

What is the basic formula to measure IOP?

Answer 73

W= P x A W is external force P is pressure inside sphere A is area.

Question 74

What law is used for applanation tonometry?

Answer 74

Imbert-Fick Law.

Question 75

What are three assumption of Imbert-Fick Law?

Answer 75

Eye is sphere, perfectly dry, and thin.

Question 76

Due to the inaccurate assumption, what is the modified Imbert-Fick Law?

Answer 76

W + S = P x A +B S is surface area B is the force required to bend the cornea.

Question 77

As you increase force, what do you see during a Goldmann's tonometry?

Answer 77

You see A and as you increase the force you eventually get the two spheres to come closer and closer. Once the inner circles are perfectly alined, you read the value and times that by 10.

Question 78

What factors increase the error when measuring IOP? (Not IOP itself)

Answer 78

Corneal thickness is an error in measurement (does not cause true difference in IOP), corneal curvature (curved cornea-need more force to push and make it flat and flat cornea-don't need to apply a lot of force),

Question 79

Will you under estimate IOP with a flat cornea or very curved cornea?

Answer 79

Flat cornea.

Question 80

Does keratoconus lead to over or under estimation?

Answer 80

Under because even though curvature is increase, central cornea gets extremely thin and flexible causing under estimation due to the cornea's decrease in strength.

Question 81

Cornea thinner, over or under estimate?

Answer 81

Under because you can easily bend it, flatten it. You don't have to push so much.

Question 82

True or False: Anything that is easy to bend, pressure is underestimate.

Answer 82

True.

Question 83

What three biomechanical properties are important factors that affect IOP measuring?

Answer 83

Rigidity, hydration, and elasticity.

Question 84

As we grow older, cornea gets hydrated, cornea gets stiffer, which means over or underestimation of IOP?

Answer 84

Over estimation.

Question 85

Is cornea elastic or visco-elastic?

Answer 85

Visco-elastic.

Question 86

Due to corneal curvature, what amount of difference is accounted?

Answer 86

1.76 mmHg.

Question 87

Due to corneal thickness, what amount of difference is accounted?

Answer 87

2.87 mmHg.

Question 88

Due to corneal biomechanics, what amount of difference is accounted?

Answer 88

17.26 mmHg.

Question 89

Pneumotonometer measures up to what amount of IOP for how long?

Answer 89

200/sec for 20 seconds.

Question 90

Pneumotonometer measures __ pulses and selects __ best to calculate IOP and pulsatile ocular blood flow.

Answer 90

7; 5.

Question 91

Pulsatile ocular blood flow represents what?

Answer 91

Choroidal circulation.

Question 92

Why is a 24 hour IOP measurement needed?

Answer 92

Certain diseases are progressive and sometimes doctors want to know if drugs are doing their job. 24 hour measurement can help with accuracy.