B10 Structure and function of the eye

• sclera

  tough, supporting wall of the eye. provides structure and protects the eye.

  
• cornea

  transparent outer layer at the front of the eye. protects eye and bends (refracts) light into the eye.

  
• iris

  contains muscles allowing it to change the diameter of the pupil and control how much light enters the eye

  
• pupil

  opening or hole in the middle of the iris allowing light to enter the eye

  
• retina

  inner surface of eye. contains receptor cells sensitive to light intensity and colour

  
• Ciliary muscles

  Attached to lens. Change shape of lens when focusing

  
• lens


  focuses light onto retina by changing shape. This ability of the lens is called accommodation.

  
• suspensory ligaments

  change shape of lens to help it focus on far and near objects

  
• optic nerve

  carries impulses from receptors on retina to brain. distance from lens to retina is 2cm

  
• Between the cornea and the lens is the aqueous humour. On the other side of the lens is the vitreous humour. Both humours are responsible for giving the eye its near perfect spherical shape. They also belong to the refractive system of the eye.

  
• Choroid

  Between the retina and sclera is the choroid. It is composed of the layers of blood vessels and connective tissue. The choroid nourishes the back of the eye with blood and nutrients.

  
• Accommodation

  The process by which the lens changes shape to focus on objects at different distances
• macula

  The macula is part of the retina at the back of the eye. It is only about 5mm across, but is responsible for our central vision, most of our colour vision and the fine detail of what we see
• fovea

  depression in the very centre of the macula where eyesight is sharpest
• blind spot

  a spot in the retina where the optic nerve connects. In this area there are no light-sensitive cells so this part of your retina can't see. We call this the blind spot.
• short-sighted

  Someone with short-sight can see near objects clearly, but cannot focus properly on distant objects.
• Short sight is caused by one of the following:

  • The eyeball being elongated - so that the distance between the lens and the retina is too great.
  • The lens being too thick and curved - so that light is focused in front of the retina.
• Short-sightedness can be corrected by placing a concave lens in front of the eye
• long-sight

  Someone who is long-sighted can see distant objects clearly, but they cannot focus properly on near objects.
• Long-sightedness is caused by one of the following:

  • the eyeball being too short - so the distance between the lens and retina is too small
  • a loss of elasticity in the lens - meaning it cannot become thick enough to focus (which is often age-related)
• Long-sightedness is corrected by putting a convex lens in front of the eye.
• Sclera ‐ Outer layer of the eye, protects the eye and keeps it in shape.