Crash Course Vision

• Light


  Electromagnetic radiation traveling in waves
• Frequency of light wave


  Determines its hue
• Amplitude of light wave

  Relates to its brightness
• Visible light is only a tiny chunk of the full electromagnetic spectrum
• Eye

  • Irregularly spherical, with an adult diameter of about 2.5 centimeters
  • Essentially hollow, full of fluids that help it keep its shape
  • Only about the anterior sixth of the whole ball is visible
• Layers of the eye wall

  • Fibrous layer
  • Vascular layer
  • Inner layer
• Cornea

  Transparent part of the fibrous layer that lets light into the eye
• Iris

  Distinctive colored part of the eye, made of smooth muscle tissue that contracts and expands to change the size of the pupil
• Lens


  Convex, transparent disc that focuses light and projects it onto the retina
• Retina


  • Contains millions of photoreceptors (rods and cones) that convert light energy into electrical signals
  • Has an outer pigmented layer and an inner neural layer with bipolar and ganglion neurons
• Optic nerve

  Carries electrical impulses from the ganglion cells in the retina to the brain's visual cortex
• Rods and cones


  • Rods are more numerous and light-sensitive, but can only register black and white
  • Cones detect fine detail and color, but are less sensitive and only active in bright conditions