The Eye and Vision

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The Eye and Vision
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Accessory Structures

• Eyebrows short,coarse hairs that help shade the
  eyes from sunlight and prevent perspiration from
  leaking into the eye.
• Orbicularis muscle allows you to frown

• Eyelids (palpebrae)
• The eyelid slit is called the palpebral fissure
• Lacrimal caruncle contains sweat and oil glands
  that produces sleep or Sandmans sand eye
  boogers

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Accessory Structures

• Eyelids cont
• Supported by connective tissue called tarsal
  plates

• Orbicularis muscles encircle the eye when they
  contract the eye closes
• Upper eyelid is larger and more motile
• Eyelid muscles contract to blink every 3-7
  seconds
• Clears eyes of debris
• Prevents drying out

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Accessory Structureseyelids cont.

• Eyelashes rich in nerve endings anything that
  touches them triggers blinking
• Tarsal (Meibomian) glands posterior to the
  eyelashes (on the eyelid)
• Produce oily secretion that lubricates eye
• Prevents lids from sticking together

• Sebaceous glands called ciliary glands lie
  between the hair follicles.
• Inflammation of these glands results in a sty

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Accessory Structureseyelids cont.

• Conjunctiva transparent mucous membrane
• Lines the eyelids and covers the white of the
  eye not the cornea
• Produces mucus
• Conjuctival sac slitlike space
• Contact lenses
• Eye meds

• Conjunctivitis pink eye

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Accessory Structures eyelids cont.

• Lacrimal Apparatus lacrimal glands and ducts
• Lacrimal gland lies in the orbit above the
  eyeball
• Continually releases a saline solution tears
• Contains mucus, antibodies and lysosomes

• Spread across eyeball and drain into the lacrimal
  punctum little red dots in the corner of the eye
• Drain into lacrimal sac and then into nasal
  cavity
• stuffiness

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Extrinsic Eye Muscles

• Eye movement controlled by 6 muscles
• Allows eyes to follow moving objects
• Maintain shape
• Hold eyeball in the orbit

• 4 run from back of the orbit to their insertion
  on the eyeball superior, inferior, lateral and
  medial rectus muscles
• Superior/inferiod oblique muscles allow for
  upward and lateral movement
• Rolling of the eyes

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• Diplopia double vision
• Strabismus cross-eyed

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Structure of the Eyeball

• Slightly irregular hollow sphere
• Wall is composed of 3 tunics (membranes the
  fibrous, vascular and sensory
• Internal cavity is filled with fluids called
  humors

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Fibrous tunic

• Outermost coat
• Composed of the sclera and the cornea
• Sclera white of the eye
• Cornea transparent bulges from the anterior of
  the sclera allows light to enter the eye

Sclera
Cornea
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Vascular Tunic

• Middle coat also called the uvea
• Pigmented
• 3 regions
• Choroid well vascularized posterior of eye
  provides nutrients to all tunics helps absorb
  light prevents light scatter

Choroid
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Vascular tunic

• Ciliary Body ring of tissue that encircles the
  lens controls lens shape
• Iris visible colored part lies between the
  cornea and the lens round central opening called
  pupil allows light into the eye

Cilary Body
Iris
Pupil
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Sensory Tunic

• Innermost tunic
• Retina 2 layers abuts the choroid and extends
  anteriorly pigmented cells (cones and rods)
  absorb light
• Cones bright light and color
• Rods dim light and peripheral images

Retina
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Sensory Tunic

• Optic disc Also called the blind spot place
  where optic nerve exits the eye lacks
  photoreceptors
• Optic nerve transmits picture to the brain

Optic Disc
Optic Nerve
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Sensory Tunic

• Fovea Centralis retinal structures are pushed
  aside light passes directly to the
  photoreceptors vision clarity

Fovea
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Internal Chambers and Fluids

• Vitreous humor clear gel that holds tremendous
  amounts of water transmits light reinforces
  eyeball
• Aqueous Humor clear fluid similar in composition
  to blood drains into the canal of Schlemm

Aqueous Humor
Vitreous Humor
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Internal Chambers and Fluids
Suspensory Ligaments

• Lens flexible structure changes shape to allow
  precise focusing of light on the retina
• held in place posterior to the iris by the
  suspensory ligament

Lens
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THE END