Internal Structure of the Eye

• Internal Structure of the eye

  
• Ciliary body


  • thickened region at the front of the choroid
  • contains the ciliary muscles which control the thickness of the lens
• Suspensory Ligament


  • connective tissue that attaches the edge of the lens to the ciliary body
• Cornea


  • dome-shaped transparent layer continuous with the sclera
  • refracts light into the eye
  • causes the greatest refraction
• Aqueous Chamber


  • space between lens and the cornea
  • filled with aqueous humour, a transparent, watery fluid
  • keeps the front of the eyeball firm and helps refract light into the pupil
• Lens


  • transparent, circular and biconvex structure
  • elastic and changes its thickness to focus light onto the retina
• Retina (innermost)


  • innermost layer of the eyeball
  • light sensitive layer which images are formed
  • contains photoreceptors which are connected to the nerve endings from the optic nerve
• Blind spot


  • region where the optic nerve leaves the eye
  • does not contain any rods or cones (not sensitive to light)
  • if image falls on the blind spot, object cannot be seen
• optic nerve


  • transmits nerve impulses to the brain when the photoreceptors in the retina are stimulated
• Fovea


  • small yellow depression in the retina where images are normally focused
  • situated directly behind the lens
  • contains greatest concentration of cones but no rods
  • allows the person to have detailed colour vision in bright light
• Vitreous Chamber


  • space behind the lens filled with vitreous humour, a transparent, jelly-like substance
  • keeps the eyeball firm and helps refract light onto the retina
• Choroid


  • middle layer of the eyeball (between the sclera and the retina)
  • pigmented black to prevent internal reflection of light
  • contains blood vessels that bring oxygen and nutrients to the eyeball and remove metabolic waste products
• Pupil reflex


  • Stimulus (change in light intensity)
  • Photoreceptors in retina
  • sensory neurone in optic nerve
  • brain
  • motor neurone
  • effector (iris muscles)
• Iris Muscles


  • The circular muscles are arranged in a circle around the pupil
  • The radial muscles radiate outwards from the pupil
  • The circular muscles and radial muscles are antagonistic
• In Bright Light (CCRR)



  • circular muscles of iris contract
  • radial muscles of iris relax
  • pupil constricts, reducing amount of light entering the eye

  
• In dim light


  • the circular muscles relax
  • radial muscles contract
  • pupil dilates, allowing more light to enter the eye