Hypermetropia

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You must have seen middle aged people holding a book away from their eyes to read properly. This is because they are not able to see the nearby objects clearly. We say that those people are suffering from hypermetropia (long sightedness).

• Hypermetropia or hyperopia is an eye defect in which distant vision is clear while near vision is blurred.
  
• This occurs when the light rays entering the eye converge behind the retina.
  
• Here you can see the formation of image in a normal eye and in a hypermetropic eye.

  

  

  
                                                  
  

• In the case of a normal eye the rays of light from the object fall on the eye and converge on the retina but in the case of a hypermetropic eye the light rays are focused behind the retina.
  

Causes of Hypermetropia

 

• Shortening of the eyeball, that is, the eyeball becomes smaller
• Increase in focal length of the eye lens

Let us now see how this defect is rectified. A long sighted eye forms image of a nearby object behind the retina. Thus, long sightedness is due to the decreased converging power of the lens. Therefore hypermetropia can be rectified by making the eye lens more convergent. This is done by placing a convex lens of suitable focal length before the eye lens as shown in the figure.