Why People Wear Glasses?

1.  A person with normal vision sees distant and close objects clearly.

2. The thickness of the eye lens is changed when looking at near or distant objects.

3.  This process is known as accommodation 

   A person who has defective vision needs spectacles to help him see clearly.

 - Two defects are:

       a)  Long-sightedness 

Light from a near object is focused behind the retina.

         b)  Short-sightedness 

Light from a far object is focused infront the retina.

As we have learnt in previous class, light can be reflected and refracted (bend). Which theory should we apply to correct this defect?

YES! REFRACTION!!!

a)  Long-sightedness 

The convex lens converges the light rays.

The converging light rays is focused onto the retina by the eye lens to form a sharp image.

    b)  Short-sightedness 

A concave lens diverges light rays before they enter the eye.

The diverging light rays is focused onto the retina 

by the eye lens to form a sharp image.

Now, let's watch this animation

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