The Eye

• The eye is an organ containing receptors sensitive to light intensity and colour.
• Label the eye.

  A) sclera

  B) retina

  C) optic nerve

  D) lens

  E) iris

  F) pupil

  G) cornea

  H) suspensory ligaments

  I) ciliary muscles

  
• The iris contains muscles which contract or relax to change the diameter of the pupil
• The pupil is a hole in the center of the iris.
• The cornea is the transparent part of the sclera and slightly refracts light.
• Suspensory ligaments and ciliary muscles change the shape of the lens.
• The lens changes shape to focus or refract light onto the retina.
• The sclera is the tough outer layer of the eye.
• The retina contains cells sensitive to light and colour [rod and cone cells]
• The optic nerve sends electrical impulses from the retina to the brain.
• In low light, the radial muscles in the iris contract to dilate the pupil, increasing the number of light rays onto the retina.
• In bright light, the circular muscles in the iris contract causing the pupil to shrink. This decreases the number of light rays on the retina.
• Cone cells must receive a strong stimulus to be activated. They are sensitive to colour / different wavelengths of light.
• Rod cells are sensitive to low light intensity.
• At night, colour vision is decreased as the stimulus is not strong enough to activate the cone cells.
• Accommodation is focusing an image from near and far.
• Myopia:

  • lens is too thick or strong / cornea too sharply curved / eye too long
  • focal point is before retina
  • corrected by concave lenses, diverging light before it reaches eye
• Hyperopia:

  • lens is too thin or weak / eye too short
  • focal point is after retina
  • corrected by convex lenses, converging light before it reaches eye