Eyes 2 - Accommodation & Visual Defects

• Which two structures refract (bend) light entering the eye? 


  Cornea

  Lens
• When light passes into the eye, where on the retina should the light be focused?

  The fovea
• When looking at a nearby object, the light from the object hits the eye at a wide angle. This means that the eye needs to refract the light strongly. 

  To achieve this, what should the shape of lens be? 

  Short and fat
• Suspensory ligament 

  
• Ciliary muscle

  
• The ciliary muscle is just like any other muscle, so it can contract or relax.
• The suspensory ligament is not a muscle, it is a ligament. 

  Can it contract and relax?

  No
• When looking at a nearby object, the lens must be short and wide to refract the light strongly and focus the light on the retina. 

  How do the ciliary muscle and suspensory ligaments achieve this? 

  The ciliary muscle contracts 

  The suspensory ligaments slacken
• The ciliary muscle is a circle band of muscle that encircles the suspensory ligaments and the lens. 

  Which of the images above, A or B, show the ciliary muscle in its contracted state? 

  You can tell it's A because the ciliary muscle (cyan layer) is much thicker, the suspensory ligaments are slackened, and the lens in much smaller than in B. 

  
• What happens to the ciliary muscle, suspensory ligaments, and the lens, when the eye focuses on a distant object?

  The ciliary muscle relaxes 

  The suspensory ligaments are pulled taut

  Lens is pulled tall and thin
• What does long-sighted mean?

  The eye is unable to focus on nearby objects 
• One solution to long-sightedness is to wear glasses.

  Which type of lens would the glasses need to contain? 

  Convex lens
• In long-sightedness, the eye can't refract the light strongly enough. The convex lens helps by refracting the light a bit before it reaches the eye.
• If somebody cannot focus on distant objects, are they long-sighted or short-sighted?

  Short-sighted