Accommodation

• How light travels in the eye

  1. Light enters the eye through the cornea which refracts the light

  2. Light then passes through the aqueous humour and the pupil

  3. The size of the pupil is adjusted by the iris to regulate the amount of light that enters the eye

  4. The light then passes through the lens which also refracts the light

  5. Light then passes through the vitreous humour and reaches the retina

  6. The retina has the photoreceptors which convert the light stimulus Into a nerve impulse

  7. Nerve impulse travels using the optic nerve to the cerebrum
• Pupillary mechanism


  The pupillary mechanism (or pupil reflex) regulates the amount of light entering the eye by adjusting the size of the pupil
• Bright light


  1. Radial muscles of the iris relax

  2. Circular muscles of the iris contract

  3. Pupil constricts (gets smaller)

  4. Less light enters the eye
• Dim light


  1. Radial muscles of the iris contract

  2. Circular muscles of the Iris relax

  3. Pupil widens (gets bigger)

  4. More light enters the eye
• Bright light

  Pupil diameter decreases (constricts)
• Bright light


  • Circular muscles contracts
  • Radial muscles Relaxes
• Bright light


  Less light enters the eye
• Dim light


  Pupil diameter increases (dilates)
• Dim light


  • Circular muscles relaxes
  • Radial muscles Contracts
• Dim light


  More light enters the eye
• Pupillary mechanism

  The process by which the size of the pupil adjusts to regulate the amount of light entering the eye
• Pupil


  The opening in the center of the iris (the colored part of the eye) that allows light to enter the eye
• Constriction


  The process by which the pupil gets smaller in response to bright light
• Dilation


  The process by which the pupil gets larger in response to low light
• Parasympathetic nervous system


  The part of the autonomic nervous system responsible for constriction of the pupil
• Autonomic nervous system


  The part of the nervous system that controls involuntary actions
• Sympathetic nervous system


  The part of the autonomic nervous system responsible for dilation of the pupil
• Bright light


  The stimulus that triggers the response of the eye's iris
• Circular muscles


  The muscles of the iris that contract (get smaller) in response to bright light, allowing less light to enter the eye
• Radial muscles


  The muscles of the iris that relax (get larger) in response to bright light, allowing more light to enter the eye
• Autonomic nervous system


  A part of the nervous system that controls involuntary actions, such as heart rate and digestion
• Sympathetic nervous system


  A branch of the autonomic nervous system responsible for the body's "fight or flight" response
• Parasympathetic nervous system


  A branch of the autonomic nervous system responsible for the body's "rest and digest" functions
• Constriction of the pupil


  A function of the parasympathetic nervous system that causes the pupil to narrow