The eye and vision

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Chapter 12

• The eye and vision

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Eyelids

• Also called palpebrae
• 4 layers thick (skin, muscle, connective tissue,
  and conjunctiva)
• Orbicularis oculi and levator palpebrae
  superioris muscles move the eyelids
• Connective tissue layer contains tarsal glands
  (or Meibomian glands) which produce oily
  secretions
• Conjunctiva-mucous membrane that covers
  everything except the cornea (see pinkeye)

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Lacrimal apparatus

• lacrimal gland secretes tears
• Superior and inferior canaliculi carry tears into
  nasal cavity
• Puncta is the opening to the canaliculi
• Canaliculi empty into lacrimal sac
• Lacrimal sac empties into nasolacrimal duct

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Diagram of lacrimal apparatus

• http//www.medicalook.com/human_anatomy/organs/Lac
  rimal_apparatus.html citation for image

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Sagittal section of eyeball
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Extrinsic eye muscles

• Superior rectus- rotates eye upward and toward
  midline
• Inferior rectus- rotates eye downward and toward
  midline
• Medial rectus- rotates eye toward midline
• Lateral rectus- rotates eye away from midline
• Superior oblique- rotates eye downward and away
  from midline
• Inferior oblique- rotates eye upward and away
  from midline
• What is strabismus? Answer coming up later.

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Extrinsic eye muscles
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Structure of eye

• Hollow ball with 3 layers
• Outer fibrous tunic
• Middle vascular tunic
• Inner nervous tunic
• ANSWER to question-strabismus is crossed eyes

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Outer tunic

• Cornea-window of the eye
• Helps focus light rays
• No blood vessels or conjunctiva
• Lots of nerve receptors so feel pain when
  something gets in your eye (slow to adapt)
• Cold receptors but no heat or touch receptors
  (thats why you can wear contacts)
• Sclera-white of eye (protects)
• Optic nerve and blood vessels pierce sclera

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Middle tunic

• Choroid coat- contains melanocytes so the coat is
  brownish/black in color
• Melanin here absorbs excess light and helps keep
  inside of eye dark
• Ciliary body forms an internal ring around front
  of eye and contains ciliary processes and ciliary
  muscles
• Suspensory ligaments extend inward from processes
  and hold lens in place

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Transverse section of eye
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Ciliary body and accommodation
distant
close

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Middle tunic continued

• Iris- colored portion of eye
• Found between cornea and lens
• Divides anterior cavity into anterior chamber
  (between cornea and iris) and posterior chamber
  (between iris and lens)
• Aqueous humor is secreted by epithelium of
  ciliary body into posterior chamber
• Also enters pupil and anterior chamber, and fills
  space between cornea and lens
• Drains through Canal of Schlemm
• Circular and radial muscles in iris control pupil
  size

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Inner tunic

• Retina contains photoreceptors
• Retina is the inner lining of eyeball that ends
  just behind ciliary body
• Ora serrata separates the visual and non-visual
  retina and is near the ciliary body
• Macula lutea- yellow spot in central retina
• Fovea centralis- depression in middle of macula
  lutea-THIS IS AREA of SHARPEST VISION

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Inner tunic continued

• Optic disc- medial to fovea centralis
• Doesnt have receptors so is the blind spot of
  the eye
• Posterior cavity-filled with vitreous humor
• Vitreous humor is not replaced

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Some links for extra help

• http//www.99main.com/charlief/Blindness.htm
• http//www.nlm.nih.gov/medlineplus/eyesandvision.h
  tml
• http//www.nei.nih.gov/health/eyediagram/