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Special Senses - Eyes
External Anatomy of the Eye
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Eyelids
Eyelashes
Conjunctiva – A membrane that lines eyelids
and covers part of the outer surface of the
eyeball
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Conjunctivitis
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Inflammation of the conjunctiva (example – pinkeye)
Caused by a bacterial or viral infection
External Anatomy of the Eye
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Lacrimal glands
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Above the lateral end of the eye
Secrete dilute salt solution (tears) onto the
anterior surface of the eyeball
Internal Anatomy of the Eye
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The eyeball is consisted of three tunics
(coats)
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Sclera – outer tunic (white of the eye)
Choroid – middle tunic (has a dark pigment that
prevents light from escaping the eye)
Retina – inner tunic (has photoreceptors called
rods and cones)
Sclera
Choroid
Retina
Internal Anatomy of the Eye (cont.)
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Photoreceptors – respond to light
Rods
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Detect black and white
Process dim light
Used for peripheral vision
120 million rods in one eye
Cones
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Detect color
Process bright light
Most are found in the center of the retina
7 million cones in one eye
Internal Anatomy of the Eye (cont.)
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Optic nerve – sends information from the
eyes to the brain
Optic disk – part of the eye where optic
nerves travel through
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Does not have any photoreceptors
Known as the blind spot
Fovea centralis
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Near the optic disk that contains only cones
The area of sharpest vision
Internal Anatomy of the Eye (cont.)
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Cornea – Clear membrane that forms the
front of the eye
Iris – pigmented portion of the eye
Pupil – The expanding and contracting
opening in the iris through which light passes
to the retina
Cornea
Pupil
Iris
Internal Anatomy of the Eye (cont.)
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Lens
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Allows light to reach the retina to focus an image
Held in place via suspensory ligaments
Lens
Suspensory
ligaments
Internal Anatomy of the Eye (cont.)
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The lens divides the eye into two chambers
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Aqueous humor – Anterior segment that contains
a clear watery fluid
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Provide nutrients for the lens and cornea which lack a
blood supply
Vitreous humor – Posterior segment that’s filled
with a gel-like substance
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Helps prevent the eyeball from collapsing inward by
reinforcing it internally
Pathway of Light Through the Eye
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Cornea
Aqueous humor
Pupil
Lens
Vitreous humor
Retina
Choroid
Optic disk
Optic nerve
Malfunctions of the Eyes
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Cataract
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As one ages, the lens becomes hard and cloudy.
Causes vision to become hazy and possibly
blindness
Malfunctions of the Eyes
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Glaucoma
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If drainage of aqueous humor is blocked, pressure
within the eye increases dramatically compressing
the retina and optic nerve.
This can cause pain and possibly blindness.