The Eye

• the eye is a sense organ
• parts of the eye

  A) retina

  B) sclera

  C) optic nerve

  D) lens

  E) cornea

  F) pupil

  G) iris

  H) ciliary muscles/suspensory ligaments

  
• functions of the eye

  • sclera - tough outer supporting layer
  • retina - made up of light
  • optic nerve - carries impulses from retina to brain
  • ciliary muscle & suspensory ligaments - changes shape of lens to focus light rays on retina
  • lens - focuses light rays on retina
  • cornea - refracts light bends on the eye
  • iris - muscles controlling size of pupil
  • pupil - controls amount of light in eye
• accommodation

  when the eye adjusts its focus to see objects clearly at different distances
• when focusing on a near object

  • ciliary muscles contract
  • suspensory ligaments loosen
  • thin lens
  • strong level of refraction
• when focusing on a distant object

  • ciliary muscles relax
  • suspensory ligaments tighten
  • thick lens
  • slight level of refraction
• focusing on objects

  A) distant

  B) near

  
• myopia

  short sightedness unable to focus on distant objects
• hyperopia

  long sightedness unable to focus on near objects
• myopia occurs when the eyeball is too long or the cornea is too sharply curved
• hyperopia occurs when eyeball is too short or cornea is not curved enough
• lens used for each condition

  A) concave

  B) convex

  
• treatments for vision defects

  • contact lenses
  • laser eye surgery
  • replacement lens surgery
• contact lenses

  • advantages - clear vision without using glasses, a wider field view
  • disadvantages - regular cleaning and maintenance , discomfort/dryness
• glasses

  • advantages - correct vision problems / help people see clearly
  • disadvantages - inconvenient at times , unfavourable in weather conditions
• laser eye surgery

  • advantages - dont need glasses or lenses , quick recovery
  • disadvantages - possibility of experiencing glares , dry eyes/discomfort in procedure
• replacement lens

  • advantages - no chance of rejection
  • disadvantages - carries higher risks than laser eye surgery