the eye

• Cornea is a transparent lens that refracts light to focus it on the retina.
• Iris controls how much light enters the pupil.
• Lens is a transparent disc that can change shape to focus light onto the retina.
• Retina contains light receptor cells:

  • Rods detect light intensity.

  • Cones detect colour.
• When an object is close up:

  • Ciliary muscles contract.

  • Suspensory ligaments loosen.

  • Lens becomes wider and more light is refracted.
• When an object is far away:

  • Ciliary muscles relax.

  • Suspensory ligaments tighten.

  • Lens becomes thinner and less light is refracted.
• In dim light, pupils dilate in order to allow as much light into the eye as possible to improve vision.
• In bright light, pupils constrict in order to prevent too much light from entering the eye and damaging the retina.
• Dim light:

  • Radial muscles contract.

  • Circular muscles relax.
• Bright light:

  • Radial muscles relax.

  • Circular muscles contract.
• Diagram of eye when object is close up:

  
• Diagram of eye when object is far away:

  
• Short-sightedness (myopia):

  • Lens is more curved than normal or eyeball is too long.

  • Light is refracted too much.

  • Focal point falls in front of the retina.

  • Corrected with a concave lens.
• Diagram of the eye when it has short-sightedness:

  
• Diagram of the eye when a concave lens is used for myopia:

  
• Long-sightedness (hyperopia):

  • Lens is less curved than normal or eyeball too short.

  • Focal point falls behind retina.

  • Light not refracted enough.

  • Corrected with convex lenses.
• Diagram of eye when it has long-sightedness:

  
• Diagram of eye when a convex lens is used for hyperopia:

  
• Colour blindness is when cones in retina don’t work properly.
• Cataracts is a condition in which build-up of protein causes clouding of the lens and light is dispersed or blocked.

  Can be corrected by replacing cloudy lens with an artificial one.