Eyes 1 - Structure of the Eye & Iris Reflex

• What is the cornea? 

  A transparent layer at the front of the eye which refracts light
• what is 'x'?

  optic nerve

  
• retina

  
• What is the pupil? 

  The gap through which light passes to reach the lens
• lens

  
• What are the names of the two types of receptor cells in the retina? 

  Cone cells 

  Rod cells
• Which light-sensitive cells in the retina enable you to see in colour?

  Cone cells
• The eye is a sense organ. Which two stimuli are the receptor cells of the eye sensitive to?

  Colour 

  Light intensity 
• Which light sensitive cells in the retina enable you to see in the dark?

  Rod cells
• Rod cells are very sensitive, but can only detect the presence or absence of light. This means they help us see in low light environments like night time, but they can't see in colour.
• The point where light focuses on the retina is called the fovea. This region contains the highest concentration of cone cells and gives the sharpest image.

  
• What is the purpose of the iris reflex?

  To ensure the optimum amount of light enters the eye
• When the pupil is very large, do we describe it as 'constricted' or 'dilated'? 

  Dilated 
• Which two muscles make up the iris? 

  Radial muscles 

  Circular muscles 
• When the eye is exposed to bright light, will the pupil constrict or dilate?

  Constrict 
• What happens to the circular and radial muscles when the pupil constricts?

  The circular muscle contracts 

  The radial muscle relaxes 
• Too much light can damage your retina, so in bright light, your pupil will constrict to let less light through. 
• Cornea : Refracts light - bends it as it enters the eye

  Iris: Controls how much light enters the pupil

  Lens : Further refracts light to focus it onto the retina

  Retina : Contains the light receptors

  Optic nerve : Carries impulses between the eye and the brain

  Sclera: Tough white outer layer of the eye. It helps protect the eye from injury