Distinguish between myopia and hypermetropia. Show diagrammatically how these defects can be corrected.

Question

Solution

• Nearsightedness or Myopia − A person suffering from myopia can see only nearby objects clearly, but cannot see the objects beyond a certain distance clearly.

Myopic eye:

Correction − In order to correct the eye for this defect, a concave lens of suitable focal length is placed close to the eye so that the parallel ray of light from an object at infinity after refraction through the lens appears to come from the far point P'of the myopic eye.

• Farsightedness or Hypermetropia − A person suffering from hypermetropia can see distant objects clearly, but cannot see nearby objects.

Hypermetropic eye:

Correction − To correct this defect, a convex lens of suitable focal length is placed close to the eye so that the rays of light from an object placed at the point N after refraction through the lens appear to come from the near point N'of the hypermetropic eye.