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OPTM 5032 - Ocular Physiology > Aqueous Humor Dynamics > Flashcards

Aqueous Humor Dynamics Flashcards

1
Q

Three methods of aqueous humor secretion?

A

Diffusion

Ultrafiltration

Secretion

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2
Q

When is aqueous humor production greatest?

A

In the morning (2.97 +/- 0.77 microlitre per min)

(8 am - noon)

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3
Q

When is the lowest production of aqueous humor?

A

At night (1.28 +/- ul per min)

(midnight to 6:00 am)

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4
Q

Na+K- ATPase is predominatly bound to?

A

Plasma membrane of non-pigmented epithelium

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5
Q

Na+ ions from the Na+K-ATPase are pushed where?

A

Into the posterior part of anterior chamber to which the water follows

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6
Q

Aqueous Humor Outflow via Trabecular outflow

A

70-95%

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7
Q

Aqueous Humor outflow via uveoscleral outflow?

A

5-30%

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8
Q

True or False: Aqueous Humor Outflow and trabecular outflow increase with age?

A

False

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9
Q

Factors that affect IOP: long term

A

Genetics

Age (IOP increases with age)

Gender (M=F 20-40; F > inc. 40)

Seasonal (Winter > Summer) (Weight)

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10
Q

Factors affecting IOP: Short Term

A

Diurnal variations (time of day, higher in the morning)

Postural variations (supine can cause increase)

Exercise (decrease)

Blinking and forceful closure (increase)

Activities causing Valsalver maneuver (exhale with mouth closed)

Eye movements

Food and Drugs

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11
Q

What kind of fluid was Aqueous Humor considered to be in the early 20th century?

A

Stagnant

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12
Q

Why do we need aqueous humor?

A

Shape, Optical Properties

Nourishment to cornea and lens

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13
Q

What is the refraction of the aqueous humor?

A

1.33332

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14
Q

Is the aqueous humor vascular or avascular?

A

Avascular

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15
Q

How does the aqueous humor have nutrients within it?

A

Since it is avascular the amount of nutrients within the aqueous humor depends on it’s constant turnover.

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16
Q

What else does the constant turnover of aqueous humor do?

A

Wash out metabolic waste products

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17
Q

What do the longitudinal fibers of the ciliary body muscles do?

A

Attach ciliary body to limbus

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18
Q

What do the circular fibers of the ciliary body muscles do?

A

Attach to the anterior and inner portions of the ciliary body

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19
Q

What do the radial fibers of the ciliary body do?

A

Connect longitudinal and circular fibers

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20
Q

What are the 3 main vessels of the ciliary body?

A

Episcleral circle

Intramuscular Circle

Major Arterial Circle

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21
Q

Where is the Major Arterial Circle and what does it supply?

A

Lies near the iris root; Is the primary supply of the iris and ciliary body

(Paralimbal branch of the LPCA)

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22
Q

The Ciliary Process is supplied by which two branches of the MAC?

A

Anterior ciliary process arteriole

Posterior Ciliary Process Arteriole

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23
Q

What is a ciliary process?

A

The functional unit responsible for production of aqueous humor secretion

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24
Q

What are ciliary processes made of?

A

1) Capillaries
2) Stroma
3) Epithelia

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25
Q

What portion of the ciliary process do the capillaries occupy?

A

The center of each process

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26
Q

What are the two layers of ciliary epithelium surrounding the stroma?

A

Pigmented and Nonpigmented epithelium

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27
Q

What are some functions of Aqueous Fluid?

A

Source of antioxidants

Carries oxygen

Maintain globe shape

Shock absorption

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28
Q

What makes aqueous humor fluid?

A

Carefully controlled filtrate of blood produced by ciliary body

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29
Q

Which chamber of the anterior chamber does the aqueous humor flow into after secretion?

A

The posterior chamber

30
Q

Where does it go after being secreted into the posterior chamber?

A

Aqueous humor flows around the crystalline lens and through the pupil to the anterior chamber of the anterior chamber?

31
Q

Does the rate of aqueous humor production follow a pattern?

A

Yes, it shows a circadian rhythm

32
Q

How much aqueous humor is produced in the morning as opposed to night time?

A

In the morning there is much more production.

(2.97 uL/min vs. 1.28uL/min)

33
Q

Is aqueous humor an active or a passive process?

A

Active, It works against the concentration gradient

34
Q

What two enzymes are involved in aqueous formation?

A

Na,K-ATPase (bound to NPE; pushes Na+ into posterior chamber so water follows)) and Carbonic Anhydrase

35
Q

What happens if you inhibit either enzyme?

A

Decreases aqueous production

36
Q

What are the two pathways in which aqueous humor exits the eye?

A

Trabecular

Conventional

37
Q

Trace the trabecular pathway

A

Trabecular Meshwork

Inner wall of schlemm’s canal into its lumen

Collector channels

Aqueous Veins

Episcleral Venous Circulation

38
Q

Trace the unconventional/uveoscleral/posterior route

A

Iris Root

Uveal Meshwork

Anterior face of ciliary muscle

Through the connective tissue between muscle bundles

Suprachoroidal space

Sclera

39
Q

What percent of aqueous humor outflows through each pathway?

A

Trabecular: 70-95%

Uveoscleral: 5-30%

40
Q

How does aging affect aqueous humor outflow?

A

Both total and trabecular outflow decline with age

41
Q

Capillaries of the ciliary processes and choroid are ______.

A

Fenestrated

42
Q

How are the RPE, NPE and ciliary processes joined together?

A

Via tight junctions which create a blood aqueous barrier

(Selective to intermediate and high molecular weight substances)

43
Q

Does the endothelia of the inner wall of Schlemm’s canal also have tight junctions?

A

Yes, it prevents the movement of fluid and solutes from the Canal of Schlemm into the trabecular meshwork and anterior chamber

44
Q

The iris and retina do not possess tight junctions/similar epithelia to the blood aqueous barrier but remain impermeable. How?

A

They have nonfenestrated capillaries

45
Q

IOP is the outcome of what?

A

Inflow/outflow of aqueous humor

46
Q

If plasma components increase in the anterior chamber IOP will increase or decrease?

A

Increase

47
Q

How do diseases, trauma or drug induced breakdown of the blood aqueous barrier affect IOP?

A

Increases IOP

48
Q

How does the eye combat breakdown of the blood aqueous barrier?

A

Inflow by ultrafiltration is suppressed and thus reduces the rise in IOP

This is kown as Pseudofacility

49
Q

How else is IOP rise combatted in the breakdown of the blood aqueous barrier?

A

Inflammation; possibly interferes with the active transport mechanisms

50
Q

How is IOP measured?

A

Using a tonometer

51
Q

What is the mean IOP in people ages 10-69?

A

15.8 with a standard deviation of 2.57

52
Q

What is the IOP magic number?

A

21 (Mean +2SD)

53
Q

Does IOP increase or decrease with age?

A

Increase

54
Q

When do females begin to see greater increases in IOP?

A

Post 40 years of age

55
Q

Does refractive error have anything to do with the pressure of the eye?

A

NOPE!!!

56
Q

Is IOP greater in the winter or summer?

A

Winter because people are less active and thus gain weight and increase their BMI

57
Q

What short term factors can affect your IOP?

A

Diurnal Variations

Postural Variations (supine = increase)

Exercise (decrease)

Forceful closure of eyes (increase)

Valsalver Maneuver (exhale with mouth closed = increase)

Eye Movements

58
Q

How does Alcohol affect IOP?

A

Decrease

59
Q

How does caffeine affect IOP?

A

Slight increase

60
Q

How does Tobacco affect IOP?

A

May cause transient increase

61
Q

How do Heroine and Marijuana affect IOP?

A

Decrease

62
Q

What does tonometry do?

A

Measure pressures

63
Q

What are the conditions of the Imbert-Fick Law?

A

Perfect Sphere

Dry

Infinitely Thin

(Pretty much impossible)

64
Q

Factors affecting IOP measurements.

A

Central corneal thickness

Corneal curvature

Aging

IOP effects on cornea

Biomedical Properties (Rigidity, Hydration, Elasticity)

65
Q

What is Hysteresis and how is it applied to the eye?

A

These are visco-elastic materials (like foam matresses); this applies to the eye because the Cornea is also visco-elastic

66
Q

How does corneal curvature affect pressure estimates?

A

Steeper = overestimate

Flatter = underestimate

(Not a huge factor)

67
Q

How does Corneal thickness affect IOP estimates?

A

Thicker = overestimate

Thinner = underestimate

Not a huge factor

68
Q

How does rigidity affect IOP estimates?

A

Explains over 17mm of variance

69
Q

What does pulsatile blood flow represent?

A

It is a calculated value that represents choroidal circulation

70
Q

What is intraocular pressure telemetry used for?

A

24-hour IOP measurement; helps identify spikes in IOP both short and logn term of various drugs

Evaluate clinical efficacy

71
Q

Two types of telemetry

A

Non-invasive (temporary (contact lens))

Invasive (Permanent implant)

OPTM 5032 - Ocular Physiology (9 decks)

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