The human eye and the colorful world long 3

Question 1

What is Hypermetropia ?

Answer 1

A person with hypermetropia can see distant objects clearly but cannot see nearby objects
distinctly. The near point, for the person, is farther
away from the normal near point (25 cm). This is because the light rays from a close by object are focused at a point behind the retina. This defect arises either because

(i) The focal length of the eye lens is too long
(ii) The eyeball has become too small.

This defect can be corrected by using a convex
lens of appropriate power.

Question 2

What is Presbyopia ?

Answer 2

The power of accommodation of the eye usually
decreases with ageing. They find it difficult
to see nearby objects comfortably and distinctly
without corrective glasses. This defect is
called Presbyopia. It arises due to the gradual
weakening of the ciliary muscles and diminishing flexibility of the eye lens.

Question 3

What are bi-focal lenses

Answer 3

Sometimes, a person may suffer from both myopia and hypermetropia. Such people often require bi-focal lenses. A common type of bi-focal lenses consists of both concave and convex lenses. The upper portion consists of a concave lens. It facilitates distant vision. The lower part is a convex lens. It facilitates near vision.