physics

• Parts of the human eye

  • Cornea
  • Pupil
  • Iris
  • Sclera
  • Lens
  • Retina
  • Optic Nerve
  • Blind Spot
• Cornea


  Transparent covering of the front of the eye, allows for the passage of light into the eye and functions as a fixed lens
• Pupil


  Black hole in iris where light enters
• Iris


  Colored, circular muscle that controls the amount of light entering the eye
• Sclera


  Tough white skin that covers all of the eyeball except the cornea, supports the eyeball and provides attachment for muscles
• Lens


  Converging lens that allows us to see objects near and far
• Retina


  Internal membrane that contains light-receptive cells (rods and cones) and converts light to electrical signals
• Optic Nerve


  Transmits electrical impulses from retina to the brain
• Blind Spot


  Small spot on the back of the retina where the optic nerve leads back into the brain, with no rod or cone cells, compensated for by the other eye
• Pupil size control


  Pupil gets larger when eye needs more light, pupil gets smaller when eye needs less light which makes it directly proportional
• The cornea allows for the passage of light into the eye and also focuses the light
• The iris controls the amount of light entering the eye
• The sclera supports the eyeball and provides attachment for muscles
• The lens allows us to see objects near and far
• The retina converts light waves to electrical signals
• The optic nerve transmits electrical signals from the retina to the brain
• The blind spot is an area on the retina with no rod or cone cells, compensated for by the other eye
• Cornea and lens


  The two lenses in the eye, with the cornea doing most of the focusing and the lens providing adjustable fine-tuning
• How the lens focuses

  Lens has a small depth of field, can focus on near or far objects but not both at the same time, by changing the bulge of the lens
• Less bulgy lens


  Teacher is in focus, thumb is out of focus
• More bulgy lens


  Thumb is in focus, teacher is out of focus
• 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, corrected 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 that affect the optic nerve and pressure, leading to loss of ganglion cells and gradual loss of sight and eventual blindness, 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
• The human mind does not read every letter by itself, but the word as a whole