Parts of eye

• CORNEA 

  (clear lens in front of eye)

  • transparent covering of the front of the eye
  • Allows for the passage of light into the eye and functions as a fixed lens.
  • allows for the passage of light into the eye and it also focuses the light
• PUPIL (black hole)

  • black hole in iris
  • where light enters
  • the hole where light enters into the eye
• Pupil Size - is controlled by iris muscles
• PUPIL

  • When the eye needs more light to enter (when it is dark), the pupils get larger; allowing more light to enter the eye
  • When the eye needs less light to enter (when it is very bright), the pupils get smaller; allowing less light to enter the eye
• IRIS 

  (colored part)

  • colored part of eye
  • controls light entering
  • colored, circular muscle
  • controls the amount of light entering the eye
• SCLERA

  (white part)

  • whites of the eye
  • supports eyeball
  • provides attachment for muscles
  • a tough white skin (made of tissue) that covers all of the eyeball except the cornea.
  • supports eyeball and provides attachment for muscles
• LENS 

  (lens behind pupil)

  • converging lens
  • allows us to see objects near and far
• RETINA

  • internal membrane
  • contains light-receptive cells (rods and cones)
  • converts light to electrical signals
• OPTIC NERVE

  • Transmits electrical impulses from retina to the brain
  • Creates blind spot
  • Brain takes inverted image and flips it so we can see
• Blind Spot

  • On retina where optic nerve leads back into the brain
  • No rod or cone cells
  • Other eye compensates for this area
• Blind Spot Function

  • Small spot on the back of the retina
  • Other eye compensates for this area
•  Your 2 Lenses: Cornea and Lens

  • There are two lenses in your eye, the cornea and the lens.
  • The cornea, the front surface of the eye, does most of the focusing in your eye
  • The lens provides adjustable fine-tuning of the focus 
• How Lens Focus

  • Your lens has a small depth of field 
  • You can't see something close and far with both objects in focus at the same time
  • Hold out your thumb about a foot away from your eye
  • Then, alternately focus on thumb and me (right above your thumb)
  • Note that you cannot see both me and your thumb sharply (in focus) at the same time
  • You focus on one or the other by changing the bulge of your lens
• HYPEROPIA

  • Far-sightedness
  • Problem seeing close objects
  • Distance between lens and retina too small
  • Light focused behind retina
  • Corrected with converging lenses
• PRESBYOPIA

  • Form of far-sightedness
  • Harder for people to read as they age
  • Lens loses elasticity
  • Corrected by glasses with converging lenses
• MYOPIA

  • Near-sightedness
  • Problem seeing objects far away
  • Distance between lens and retina too large
  • Light focused in front of retina
  • Correct with diverging lenses
• ASTIGMATISM

  • Eye cannot focus an object’s image on a single point on retina
  • Cornea is oval instead of spherical
  • Causes blurred vision
  • Some types can be corrected with lenses
• GLAUCOMA

  • Group of diseases
  • Affects optic nerve - pressure
  • Loss of ganglion cells
  • Gradual loss of sight and eventual blindness
  • Check eyes regularly
  • Can be treated
• CATARACTS

  • Clouding forms in lens due to denaturing of lens protein
  • Obstructs passage of light
  • Caused by age, chronic exposure to UV, or due to trauma
  • Removed by surgery
• CONTACT LENSES

  • Artificial lens placed over cornea
  • Same as glasses
  • Corrects for both near and far-sightedness
  • Also used for cosmetic purposes (eye colour, Hollywood) 
• Sclera -- Cornea -- Iris -- Pupil -- Lens -- Retina -- Optic Nerves