Eye notes

• Structure of the eye

  • conjunctiva
  • ciliary body
  • cillary muscles
  • pupil
  • aqueous humour
  • Iris
  • cornea
  • lens
  • vitreous humour
  • sclera
  • choroid
  • retina
  • yellow spot
  • S-A
  • eyebrows
  • eyelashes
• Sclera


  • Tough, non-elastic, opaque outer covering
  • In front, the opaque sclera becomes specialised as a transparent disc called the cornea, which is a part of the sclera
• Choroid


  • Middle layer, contains blood vessels and a brown pigment
  • Continuous with the ciliary body and the iris
  • Ciliary body contains the ciliary muscles
  • Iris may be coloured blue, green, or brown etc. and gives the eye its colour
  • Opening in the centre of the iris is the pupil
• Retina


  • Innermost layer of the eye
  • Made up of two types of light receptor cells: rods and cones
  • Nerve fibres from the rods and cones leave the eye as the optic nerve, which carries impulses to the brain
  • Yellow spot has a very high concentration of cones without rods, it is the centre of the clearest vision
  • Blind spot contains no rods and cones and is therefore not sensitive to light
• Lens


  • Refracts light rays entering so as to focus them on the retina
  • Shape of the lens can be altered for near or distant vision
• Functioning of the eye (C.A.P.L.V.)

  1. Light reflected from the object passes through the cornea, aqueous humour, pupil, lens and vitreous humour and falls on the retina where image is formed

  2. Photoreceptors (Rods and Cones) receive light stimulus

  3. Stimulus is converted into nerve impulses

  4. Nerve impulses are carried by optic nerve to cerebrum where impulses are interpreted
• Accommodation


  1. For near vision: Ciliary muscles contract, suspensory ligaments become slack, tension on the lens decreases, lens becomes more convex, refractive power of the lens is increased

  2. For distant vision: Ciliary muscles relax, suspensory ligaments become taut, tension on the lens capsule increases, lens becomes less convex, refractive power of the lens is decreased
• Visual defects


  • Short-sightedness (myopia)
  • Long-sightedness (hyperopia)
  • Astigmatism
  • Cataract
• Short-sightedness (myopia)


  Inability of lens to become more flat/eyeball is longer than normal, lens bends the light rays too much, as a result it falls in front of the retina causing the image to be blurred, cannot see distant objects clearly
• Long-sightedness (hyperopia)


  Inability of lens to become more convex/eyeball is shorter than normal, lens does not bend light rays enough, as a result it falls behind the retina causing the image to be blurred, cannot see near objects clearly
• Astigmatism


  The curvature of the lens, or cornea is uneven resulting in distorted images
• Cataract


  Lens becomes cloudy and opaque
• Significance of binocular vision