eye

• converts light into impulses
• Bones eyelids eyelashes - protect from mechanical damage
• 6 external muscles control the movement of the eyeball to make sense of the surroundings
• Lacrimal glands produce salty tears that keep the conjuntive moist and wash away dust
• Meibomian glands secrete oily substance that lubricates the eyeball
• Sclera:

  tough and inelastic helps maintain the shape of the eyeball
• Lens:

  round and flexible

  thin/flat or bulging on where the image
• Pupil:

  allows light in eye
• Cornea:

  front layer of sclera

  transparent so it allows light to travel

  bulges and refracts
• Conjunctiva:

  membrane covering the front of the eye

  pain receptors to protect from foreign objects
• Anterior cavity:

  liquid substance - Aqueous fluid

  provides nutrients and oxygen to lens and cornea

  carries away wastes
• Iris:

  front part of choroid

  controls amount light entering eyeball
• Ciliary bodies:

  ring of muscles

  holds suspensory ligaments
• Suspensory ligaments:

  holds lens in place

  attached to ciliary muscles
• Retina:

  contains photo receptors that convert light into nerve impulses
• Posterior cavity:

  filled with vitreous humour a jelly like substance that provides support and pressure for the eye to prevent it from collapsing
• Choroid

  dark layer contianing blood vessels to nourish the retina
• Fovea:

  place on retina where image is the clearest because there are only cones
• Blindspot:

  area where optic nerve leaves the eyeball - no photo receptors
• Photoreceptors:

  • cones: Bright light, clear images, allow us to see colour, mainly on fovea
  • Rods: dim light, black and white, peripheral area on retina
• Accommodation the ability of the eye to focus on objects by changing the shape of the lens
• Close vision:

  1. Image needs to be refracted more
  2. Ciliary muscles contract
  3. Suspensory ligaments slacken/loosen
  4. Lens bulges
  5. Light is refracted more so it falls on the fovea
• Far Vision:

  1. Image needs to be refracted less
  2. ciliary muscles relax
  3. suspensory ligaments tighten
  4. lens becomes thinner
  5. image is refracted less so image falls on fovea
• Pupillary Mechanism:

  • Bright Light: controlled by parasympathetic nervous system

  1. Circular muscles contract
  2. Radial Relax
  3. Pupil constricts

  • Dim light: sympathetic nervous system

  1. Circular muscles relax
  2. radial contract
  3. Pupil dilates
• Binocular vision:

  each eye sees a different image and the brain puts together 3D image
• How images are formed:

  • refraction at cornea
  • lens changes and adjusts - accommodation
  • visual association area perceives the image right way up
• Myopia:

  image is bent too much so the image doesn't fall on fovea

  short sightedness

  WHY

  • lens can't get thin enough
  • eye too long
  • cornea too round

  Concave lens
• Hyperopia:

  image isn't bent enough image falls behind the retina - longs sightedness

  WHY:

  • eyeball too short
  • cornea too flat
  • lens can't bulge enough enough
• Astigmatism:

  surface of lens or cornea isn't perfectly smooth treated with contacts or glasses
• Cataracts:

  clouding of lens with old age, gradual loss of vision, can be caused by UV light

  treated with surgery