Aqueous Humor Flashcards
Learn all about the physiology of the aqueous humor, including its formation and issues with IOP.
What are the primary purposes of aqueous humor?
1) Maintain globe shape
2) Nourishment & waste removal for the avascular cornea & lens.
3) Source of antioxidants for corneal epithelium & lens
4) Shock Absorber
Refractive index of aqueous humor is…?
1.333
Aqueous humor is secreted by which part of the eye?
ciliary epithelium of ciliary process
Name the 3 vascular circles in the ciliary body.
Episcleral circle
intramuscular circle
major arterial circle (near iris root)
Ciliary process is supplied by which 2 branches of the Major Arteriole Circle?
Anterior ciliary process arteriole
Posterior ciliary process arteriole
Aqueous humor formation follows a _____ rhythm.
It is greatest in which part of the day?
circadian.
8am-noon, then afternoon, then least after midnight.
Which two enzymes are involved in aqueous humor formation?
Na+ K+ ATPase
Carbonic Anhydrase
What does carbonic anhydrase do?
What do inhibitors of carbonic anhydrase do?
Turns carbonic acid into CO2 & H2O.
Inhibitors can decrease aqueous humor production.
Where is Na K ATPase found?
Bound to plasma membrane of non-pigmented epithelium of ciliary process.
What are the primary and secondary pathways for aqueous humor outflow?
Primary: Trabecular meshwork route
Secondary: Uveoscleral/posterior route
The Retinal Pigmented Epithelium and the Non-PIgmented Epithelium are joined by _____ which created a ______ between the blood vessels and aqueous humor.
tight junctions
blood aqueous barrier
Which of these have fenestrated capillaries? Which have nonfenestrasted? ciliary process iris choroid retina
Fenestrated:
ciliary process
choroid
Nonfenestrated:
iris
retina
Inflow rate + outflow rate of aqueous humor = ?
Intraocular Pressure (IOP)
A breakdown in the blood aqueous barrier increases _____.
IOP
How does increased plasma components in anterior chamber and increased net inflow of fluid from blood to aqueous humor affect IOP?
Increases IOP
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?
Pseudofacility.
Decrease IOP.
Reduces secretion.
Mean IOP magic # is _____?
21
Which factors increase IOP? Which factors decrease IOP? Increased age Women over 40 Winter Supine Posture Exercise Blinking hard Alcohol, marijuana, heroin Caffeine, Tobacco
Increase: Increased age Women over 40 Winter Supine Posture Blinking hard
Decrease:
Exercise
Alcohol, marijuana, heroin
The test performed to measure IOP is called ____?
tonometry
What is this equation called?
W + S = P x A + B
What is it used for?
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)
What factors affect IOP measurements?
central corneal thickness
corneal curvature
age-related corneal changes
biomechanics (rigidity, hydration, elasticity)
The cornea’s physical properties can be described as _____?
visco-elastic
The Pulsatile Ocular Blood Flow is a calculated value that represents ______ circulation?
Choroidal
What are some reasons 24-hour IOP measurement would be helpful?
evaluate efficacy of drug testing,
check for Normal Tension Glaucoma progression,
identify IOP spikes over short & long term
What are some methods of noninvasive and temporary 24-hour IOP measurement?
contact lenses
continuous applanation or indentation devices
What are some methods of invasive and permanent 24-hour IOP measurement?
subconjunctival ante chamber implants in AC as IOL hap tics scleral buckle scleral fixated sensor post chamber implants - choroidal
80-90% of aqueous humor formation is done by which process?
Which two processes form the rest of aqueous humor?
Secretion.
Diffusion & Ultrafiltration.
What are the 4 layers of the ciliary process?
Capillaries
Strome
Pigmented Epithelia
Nonpigmented Epithelia
What kind of outflow represents 70-95% of aqueous humor outflow?
Trabecular meshwork
What kind of outflow represents 5-30% of aqueous humor outflow?
Uveoscleral
What does Na K ATPase do in aqueous humor formation?
What does this cause water to do?
Pushes Na+ ions into posterior chamber from ciliary process.
Water follows it from the ciliary process cells, contributing to aqueous humor.
Aqueous humor formation works against or with the concentration gradient?
Against.
What are the 3 muscles in the ciliary body?
longitudinal
circular
radial
The Major Arterial Circle is made of paralimbal branches of which arteries?
Long Posterior Ciliary Arteries
The longitudinal fibers attach the ciliary body to the _____?
limbus
The circular muscles are found in which portions of the ciliary body?
anterior and inner portions
The radial muscles connect which two other muscles in the ciliary body?
longitudinal and radial muscles
Which time of the day is aqueous humor produced at about 2.97 µl/min.?
8am - noon
Which time of the day is aqueous humor produced at about 1.28 µl/min.?
midnight - 6am
Which time of the day is aqueous humor produced at about 2.68 µl/min.?
afternoon
What is a pneumotonometer?
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.
What is a Perkins tonometer?
A type of portable applanation tonometer
What is applanation tonometry?
A method which measure IOP based on the force required to flatten (applanate) a constant area of the cornea.
