Download Aqueous Humor

LECTURE OUTLINE
FORMATION AND SYNTHESIS OF AQUEOUS HUMOR(GLAUCOMA)
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The Orbit
Within the Orbit: the eye (slightly smaller than a ping-pong ball
eye muscles
Lacrimal gland
cranial nerves
blood vessels
orbital fat (cushions and insulates)
The Eye is hollow
2 cavities divided by lens and ciliary bodies:
large posterior cavity
 aka vitreous body
 contains aqueous humor
small anterior cavity
 anterior chamber
 posterior chamber
The Wall of the Eye;3 layers
fibrous tunic
vascular tunic
neural tunic
i.e., retina
Fibrous Tunic
Sclera + Cornea
Functions
 mechanical support
 physical protection
 muscle attachment
 focusing
Vascular Tunic (Uvea)
contains numerous blood vessels,
lymphatic vessels,
and smooth (intrinsic) muscle
Contains:
 iris
 ciliary body
 Choroid
Functions
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provide route for blood and lymphatic supply to eyes
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regulates amount of light that enters the eye
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secretes and reabsorbs the aqueous humor within eye
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controls shape of lens, which is essential to focusing
The Iris
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The pupil is the central opening of the Iris
pupillary constrictor muscles
pupillary dilator muscles
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The Ciliary Body
consists of:
 ciliary muscle
 ciliary processes, which are folds of epithelium covering the muscle
 suspensory ligaments, attach lens to processes
The Choroid
vascular layer separating the fibrous and neural tunics dorsal to ora serrata
delivers oxygen and nutrients to the retina
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 The Neural Tunic (Retina)
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2 basic layers:
pigmented part (absorbs light)
neural part
Cavities,Segments and Chambers of Eye
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The anterior segment/cavity is the front third of the eye that includes the structures in
front of the vitreous humour
the cornea, iris, ciliary body, and lens
Within the anterior segment/cavity are two fluid-filled spaces divided by the iris plane:
the anterior chamber between posterior surface of the cornea (i.e. the corneal
endothelium) and the iris.
the posterior chamber between the iris and ciliary bodies
Aqueous Humor
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fluid that circulates within the anterior cavity (posterior  anterior chamber via
pupil)
fluid passes into posterior cavity as well
Functions Of Aqueous Humor
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Maintains the intraocular pressure and inflates the globe of the eye.
Provides nutrition for the avascular ocular tissues; posterior cornea, trabecular
meshwork, lens, and anterior vitreous.
Carries away waste products from metabolism of the above avascular ocular tissues.
May serve to transport ascorbate in the anterior segment to act as an anti-oxidant
agent.
Presence of immunoglobulins indicate a role in immune response to defend against
pathogens.
Its pressure maintains the convex shape of the cornea
Main function is to provide diopteric power to the cornea
Composition Of Aqueous Humor
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Water : 99%
Ions: HCO3-, buffers metabolic acids; Cl-, preserves electric neutrality; Na+; K+; Ca2+;
PO42Proteins: albumin, β-globulins. Very low density due to filtration.
Ascorbate; anti-oxidative, protects against UV.
Glucose
Lactate; produced by metabolism of anaerobic structures of the eye.
Amino acids: transported by ciliary epithelial cells.
Formation and Circulation of Aqueous Humor
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Aqueous humour is secreted into posterior chamber by the ciliary body, specifically the
non-pigmented epithelium of the ciliary body.
It flows through the narrow cleft between the front of the lens and the back of the iris,
to escape through the pupil into the anterior chamber
It then to drain out of the eye via trabecular meshwork.
From here, it drains into Schlemm's canal by one of two ways:
directly, via aqueous vein to the episcleral vein,
or indirectly, via collector channels to the episcleral vein by intrascleral plexus and
eventually into the veins of the orbit
Outflow of Aqueous Humor
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the aqueous humor exits the eye through the trabecular meshwork into Schlemm's
canal ,
it flows through 25 - 30 collector canals into the episcleral veins.
The greatest resistance to aqueous flow is provided by the trabecular meshwork, and
this is where most of the aqueous outflow occurs.
The secondary route is the uveoscleral drainage, and is independent of the
intraocular pressure, the aqueous flows through here, but to a lesser extent than
through the trabecular meshwork.
Intraocular pressure
Fluid Pressure:
 retains eye shape
 stabilizes position of retina
 normal 12-21 mmHg above atmospheric pressure so as to keep the eye slightly
distended.
 Regulated by balancing the production and outflow through a process of
1) Diffusion
2) Ultrafiltration
3) Active transport
Glaucoma
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Results from an abnormal increase in the intraocular pressure
Increased pressure in the intraocular
space due to either through increased production or decreased outflow of aqueous
humor
Damages the eye and the optic nerve leading to blindness.
Blind spots usually go
undetected until optic nerve is
significantly damaged.
Normal vision
Vision as it might be
affected by glaucoma
Two main categories of glaucoma:
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Open-angle glaucoma: the most common form of glaucoma - (the most common form
that affects approximately 95% of individuals)
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Closed-angle glaucoma: a less common and more urgent form of glaucoma.
 Other Types of glaucoma:
Congenital glaucoma
Juvenile glaucoma
Secondary glaucoma
Types of glaucoma – Open-angle
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Trabecular meshwork becomes less efficient at draining aqueous humor.
Intraocular pressure (IOP) builds up,which leads to damage of the opticnerve.
Damage to the optic nerve occurs atdifferent eye pressures amongdifferent patients.
Typically, glaucoma has no symptoms in its early stages.
Open-angle glaucoma is the most common form of the disease,
is progressive and characterized by optic nerve damage.
The most significant risk factor for the development and advancement of this form is high
eye pressure.
Initially, there are usually no symptoms, but as eye pressure gradually builds, at some point
the optic nerve is impaired, and peripheral vision is lost.
Without treatment, an individual can become totally blind
Types of glaucoma – Closed-angle
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Closed-angle (or narrow-angle) glaucoma:
The drainage angle of trabecular
meshwork becomes blocked by the iris.
IOP builds up very fast.
Symptoms include severe eye or brow pain,
redness of the eye,
decreased or blurred vision.
Must be treated as a medical
emergency—must visit ophthalmologist immediately.
Closed-angle glaucoma may be acute or chronic.
In acute closed-angle glaucoma the normal flow of eye fluid (aqueous humor)
between the iris and the lens is suddenly blocked.
Symptoms may include severe pain, nausea, vomiting, blurred vision and seeing a
rainbow halo around lights.
Acute closed-angle glaucoma is a medical emergency and must be treated
immediately or blindness could result in one or two days.
Chronic closed-angle glaucoma progresses more slowly and can damage the eye
without symptoms, similar to open-angle glaucoma
Detecting Glaucoma
Regular glaucoma check-ups include two routine eye tests:
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Tonometry – eye pressure test IOP
Ophthalmoscopy is a test that allows a health professional to see inside the back of the
eye (called the fundus) and other structures using a magnifying instrument
(ophthalmoscope) and a light source.
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Additional tests:
Perimetry (the perimetry test is also called a visual field test)
Gonioscopy is a painless eye test that checks if the angle where the iris meets the
cornea is open or closed, showing if either open angle or closed angle glaucoma is
present.
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