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Ocular Physio > Aqueous Humor > Flashcards

Aqueous Humor Flashcards

Learn all about the physiology of the aqueous humor, including its formation and issues with IOP.

1
Q

What are the primary purposes of aqueous humor?

A

1) Maintain globe shape
2) Nourishment & waste removal for the avascular cornea & lens.
3) Source of antioxidants for corneal epithelium & lens
4) Shock Absorber

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2
Q

Refractive index of aqueous humor is…?

A

1.333

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3
Q

Aqueous humor is secreted by which part of the eye?

A

ciliary epithelium of ciliary process

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4
Q

Name the 3 vascular circles in the ciliary body.

A

Episcleral circle
intramuscular circle
major arterial circle (near iris root)

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5
Q

Ciliary process is supplied by which 2 branches of the Major Arteriole Circle?

A

Anterior ciliary process arteriole

Posterior ciliary process arteriole

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6
Q

Aqueous humor formation follows a _____ rhythm.

It is greatest in which part of the day?

A

circadian.

8am-noon, then afternoon, then least after midnight.

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7
Q

Which two enzymes are involved in aqueous humor formation?

A

Na+ K+ ATPase

Carbonic Anhydrase

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8
Q

What does carbonic anhydrase do?

What do inhibitors of carbonic anhydrase do?

A

Turns carbonic acid into CO2 & H2O.

Inhibitors can decrease aqueous humor production.

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9
Q

Where is Na K ATPase found?

A

Bound to plasma membrane of non-pigmented epithelium of ciliary process.

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10
Q

What are the primary and secondary pathways for aqueous humor outflow?

A

Primary: Trabecular meshwork route
Secondary: Uveoscleral/posterior route

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11
Q

The Retinal Pigmented Epithelium and the Non-PIgmented Epithelium are joined by _____ which created a ______ between the blood vessels and aqueous humor.

A

tight junctions

blood aqueous barrier

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12
Q 
Which of these have fenestrated capillaries?
Which have nonfenestrasted?
ciliary process
iris
choroid
retina
A

Fenestrated:
ciliary process
choroid

Nonfenestrated:
iris
retina

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13
Q

Inflow rate + outflow rate of aqueous humor = ?

A

Intraocular Pressure (IOP)

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14
Q

A breakdown in the blood aqueous barrier increases _____.

A

IOP

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15
Q

How does increased plasma components in anterior chamber and increased net inflow of fluid from blood to aqueous humor affect IOP?

A

Increases IOP

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16
Q

When aqueous humor inflow by ultrafiltration is suppressed it is called _____?
Does this increase or decrease IOP?
This inflammatory process also reduces or increases secretion of aqueous humor?

A

Pseudofacility.
Decrease IOP.
Reduces secretion.

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17
Q

Mean IOP magic # is _____?

A

21

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18
Q 
Which factors increase IOP?
Which factors decrease IOP?
Increased age
Women over 40
Winter
Supine Posture
Exercise
Blinking hard
Alcohol, marijuana, heroin
Caffeine, Tobacco
A 
Increase:
Increased age
Women over 40
Winter
Supine Posture
Blinking hard

Decrease:
Exercise
Alcohol, marijuana, heroin

19
Q

The test performed to measure IOP is called ____?

A

tonometry

20
Q

What is this equation called?
W + S = P x A + B
What is it used for?

A

Modified Imbert-Fick Law.
Used to ascertain IOP.

W (external force)
A (area)
P (pressure inside sphere)
S (surface tension)
B (force req'd to bend cornea)
21
Q

What factors affect IOP measurements?

A

central corneal thickness
corneal curvature
age-related corneal changes
biomechanics (rigidity, hydration, elasticity)

22
Q

The cornea’s physical properties can be described as _____?

A

visco-elastic

23
Q

The Pulsatile Ocular Blood Flow is a calculated value that represents ______ circulation?

A

Choroidal

24
Q

What are some reasons 24-hour IOP measurement would be helpful?

A

evaluate efficacy of drug testing,
check for Normal Tension Glaucoma progression,
identify IOP spikes over short & long term

25
Q

What are some methods of noninvasive and temporary 24-hour IOP measurement?

A

contact lenses

continuous applanation or indentation devices

26
Q

What are some methods of invasive and permanent 24-hour IOP measurement?

A 
subconjunctival
ante chamber implants
	in AC
	as IOL hap tics
	scleral buckle
	scleral fixated sensor
post chamber implants - choroidal
27
Q

80-90% of aqueous humor formation is done by which process?

Which two processes form the rest of aqueous humor?

A

Secretion.

Diffusion & Ultrafiltration.

28
Q

What are the 4 layers of the ciliary process?

A

Capillaries
Strome
Pigmented Epithelia
Nonpigmented Epithelia

29
Q

What kind of outflow represents 70-95% of aqueous humor outflow?

A

Trabecular meshwork

30
Q

What kind of outflow represents 5-30% of aqueous humor outflow?

A

Uveoscleral

31
Q

What does Na K ATPase do in aqueous humor formation?

What does this cause water to do?

A

Pushes Na+ ions into posterior chamber from ciliary process.

Water follows it from the ciliary process cells, contributing to aqueous humor.

32
Q

Aqueous humor formation works against or with the concentration gradient?

A

Against.

33
Q

What are the 3 muscles in the ciliary body?

A

longitudinal
circular
radial

34
Q

The Major Arterial Circle is made of paralimbal branches of which arteries?

A

Long Posterior Ciliary Arteries

35
Q

The longitudinal fibers attach the ciliary body to the _____?

A

limbus

36
Q

The circular muscles are found in which portions of the ciliary body?

A

anterior and inner portions

37
Q

The radial muscles connect which two other muscles in the ciliary body?

A

longitudinal and radial muscles

38
Q

Which time of the day is aqueous humor produced at about 2.97 µl/min.?

A

8am - noon

39
Q

Which time of the day is aqueous humor produced at about 1.28 µl/min.?

A

midnight - 6am

40
Q

Which time of the day is aqueous humor produced at about 2.68 µl/min.?

A

afternoon

41
Q

What is a pneumotonometer?

A

An instrument that blows a puff of air at the cornea to cause flattening and hence measure intraocular pressure. It is commonly used in tests for glaucoma.

42
Q

What is a Perkins tonometer?

A

A type of portable applanation tonometer

43
Q

What is applanation tonometry?

A

A method which measure IOP based on the force required to flatten (applanate) a constant area of the cornea.

Ocular Physio (1 decks)

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