Science

• Eyelid


  Acts as a door, allowing light in
• Pupil


  Hole in the eye that allows light to enter
• Iris


  A muscle that changes the size of the pupil, regulating incoming light
• In dim light


  The pupil dilates
• In bright light


  The pupil constricts
• Retina


  Back layer of the eye containing light sensitive cells called photoreceptors
• Photoreceptors


  • Rods (highly sensitive to light)
  • Cones (detect color, don't function in low light)
• The image formed on the retina is upside down
• Optic nerve


  Sends messages from the retina to the brain
• Lens


  Refracts light and focuses it on the retina
• Ciliary muscles


  Change the shape of the lens to focus light on the retina
• Vitreous humor


  Fluid within the eye that refracts light and prevents the eye from collapsing
• Sclera


  The protective white outer layer of the eye
• Cornea


  A transparent portion of the sclera that allows light to enter the eye
• Choroid


  The middle layer of the eye, which absorbs light and prevents internal reflection
• Near-sightedness


  Eyes are too long, image forms in front of the retina
• Far-sightedness


  Eyes are too short, image forms behind the retina
• Concave lens


  Corrects near-sightedness
• Convex lens


  Corrects far-sightedness
• Laser eye surgery


  Laser reshapes the cornea to act as a corrective lens
• Camera eyes


  • Have a cornea, lens and retina
• Fish


  • Have lenses that stick out so they can see in every direction
• Birds


  • Have five types of cones, allowing them to distinguish more colors
• Nocturnal animals


  • Have large pupils that collect more light
  • Have a tapetum lucidum (a layer in the eye that acts as a mirror, reflecting light)
  • Have more rods than cones
• Compound eyes


  Eyes made up of smaller units called ommatidia
• Compound eyes


  • Have a convex surface so that ommatidia face out in almost all directions, allowing excellent motion detection
• Digital imaging


  Big pictures are made out of smaller elements called pixels
• Pixel


  Has a number and each number corresponds to a color
• Resolution


  The number of pixels per unit area
• Higher resolution


  Higher quality
• Charge-coupled device (CCD)


  Light falls on a grid, creating a small amount of electricity in each square. The electrical charge is converted into digital information
• Some cameras can capture other parts of the electromagnetic spectrum (Ex. infrared radiation)
• Digital information can be transmitted long distances
• Lens


  A curved piece of transparent material
• Refraction


  What happens when light rays pass through a lens
• Concave lens


  Thinner in the middle than at the edges, light rays diverge (spread out)
• Virtual image


  Formed where the apparent light rays converge, upright and smaller than the object
• As the object moves closer to the lens

  The virtual image gets larger
• Convex lens


  Thicker in the middle than at the edges, light rays converge (come together) at a focal point
• Real image


  Formed if an object is far away from the focal point, upside-down