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Biology II
07.2 Eye Anatomy: External &
Accessory Structures
Only about 1/6th of the eye can be seen.
The rest is surrounded & protected by fat & the orbit of the skull.
Leave ~ 7 – 10 lines for a diagram.
Eyelids
 Protect eye anteriorly
Medial and Lateral Canthus
 Edges of the eye
Eyelashes
Tarsal glands
 Modified sebaceous glands
 Eyelid edges
 Produce an oily secretion that lubricates the eye
Ciliary glands
 Modified sweat glands
 Found between the eyelashes
 ”Cilium” = eyelash
Conjunctiva
 Delicate membrane
 Lines the eyelids & covers part of the outer surface of the
eyeball
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 Secretes mucus to lubricate eye
Homeostatic Imbalance (p 273):
Conjunctivitis
 Inflammation of the conjunctiva
 Reddened, irritated eyes
 Pinkeye, infectious form caused by bacteria or viruses, is
highly contagious.
LACRIMAL APPARATUS
Lacrimal gland
 Located above the lateral end of each eye.
 Produces lacrimal fluid
o Dilute salt solution (tears)
o Contains antibodies & lysosomes (enzymes that destroys
bacteria)
o Protects, moistens, & lubricates the eye
Lacrimal canals
 Tears flush across the eyeball into this these canals then into the
Lacrimal sac which then goes into the Nasolacrimal duct
which empties into the nasal cavity.
 When Lacrimal secretions increase substantially tears spill over the
eyelids, fill the nasal cavities and cause “sniffles”
o Occurs when eyes are irritated or emotionally upset
Homeostatic Imbalance (p 274):
A cold or nasal inflammation often causes the lacrimal mucosa to
become inflamed and swell. This impairs the drainage of tears from
the eye surface, causing “watery” eyes.
Leave ~ 7 – 10 lines for a diagram.
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Biology II
Only 6 muscles move each eye. These muscles are well designed to
move the eye, but they are not well suited for keeping it still.
4 rectus muscles arranged in two pairs:
 Superior/inferior
 Lateral/medial
2 oblique muscles
 Superior/inferior
TYPES of EYE MOVEMENT
Conjuctive
 Both eyes move in same direction
 Saccades: very fast & accurate, used to fixate a peripheral
target
 Smooth pursuit: maintains fixation on a moving target
Vergence
 Eyes move in opposite directions
 Used to track an object moving in depth
 Closely coordinated with accommodation
Remember to:
Reduce, Recite, Reflect, & Review!
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