The eye

• What is the sclera

  Tough supporting wall of the eye
• what is the cornea

  Transparent outer layer , it refracts light into the eye
• what is the iris

  contains muscles that allow it to control the diameter of the pupil

  so it controls how much light enters the eye
• what is the lens

  focuses light on to the retina
• what is the retina

  contains light receptor cells sensitive to light and colour
• what do the ciliary muscles and suspensory ligaments do

  control the shape of the lens
• what is the optic nerve

  carries impulses from the receptors to the brain
• iris reflex (bright light)

  light receptors detect bright light

  circular muscles contract

  radial muscles relax

  reduces the amount of light that can enter the eye
• iris reflex (dim light)

  radial muscles contract

  circular muscles relax

  makes the pupil wider
• why is there an iris reflex

  very bright light can damage the retina
• how does the eye focus on close objects

  the ciliary muscles contract, which slackens the suspensory ligaments

  the lens becomes fat

  this increases the ammount by which it refracts light
• How does the eye focus on distant objects

  The ciliary muscles relax, the suspensory ligaments pull tight

  the lens go thin

  light is refracted by a smaller ammount