Farsightedness or Hypermetropia: Hypermetropia is the defect of eye in which a person can see only farther objects but fails to see nearer objects distinctly. This defect is due to
(a) Increase in focal length of eye lens.
(b) Contraction of eye-sphere.
Due to these reasons the image of a nearby object is formed behind the retina.
Remedy: The near point of hypermetropic eye is displaced from D = 25cm to some distant point. To eliminate this defect a convex lens of suitable focal length is used. The equivalent focal length of corrective convex lens and eye lens should be decreased to a value such that the distinct image of nearby objects is formed at the retina. Suppose the near point of a normal eye is at N and that of a hypermetropic eye is at O. The corrective convex lens forms the image of near point (N) at point O, then this image will act as the object for eye lens and the final image (I) will be formed at the retina.Therefore the corrective lens enables to form the distinct image of near point (N) at retina
