Eye

• Eye

  • Attached to skull by rectus muscles
  • 3 layers: sclera, choroid, retina
  • Cornea refracts light
  • Iris controls pupil size
  • Lens focuses light
  • Ciliary muscles control lens curvature
  • Suspensory ligaments attach lens to ciliary muscles

  
• Photoreceptors


  • Rods for dim light, black and white
  • Cones for bright light, colour
• Fovea

  Site where images are focused, most photoreceptors
• Blind spot

  Site where optic nerve leaves eye, no photoreceptors
• Pupil reflex

  1. Change in light intensity stimulates retinal photoreceptors

  2. Nerve impulses transmitted to brain

  3. Brain transmits nerve impulses to iris muscles

  4. Circular muscles contract, radial muscles relax in bright light (pupil constricts)

  5. Circular muscles relax, radial muscles contract in dim light (pupil dilates)

  
• Focusing on near objects

  1. Ciliary muscles contract, relaxing suspensory ligaments

  2. Lens becomes thicker and more convex, decreasing focal length

  3. Light rays bend more, focus on retina

  4. Photoreceptors stimulated, nerve impulses to brain

  
• Focusing on distant objects

  1. Ciliary muscles relax, suspensory ligaments pull taut

  2. Lens becomes thinner and less convex, increasing focal length

  3. Light rays bend less, focus on retina

  4. Photoreceptors stimulated, nerve impulses to brain