To restore clear vision in persons whose size of the eye ball has reduced, he/she is suggested to use suitable

As stated in the chapter (Section 10.2 b, Hypermetropia), 'This defect arises either because (i) the focal length of the eye lens is too long, or (ii) the eyeball has become too small.' When the eyeball is too small (reduced), the retina lies closer to the lens than normal, so light rays from a nearby object are focussed at a point behind the retina — the image cannot form on the retina itself. The NCERT text further states: 'This defect can be corrected by using a convex lens of appropriate power... Eye-glasses with converging lenses provide the additional focussing power required for forming the image on the retina.' A converging (convex) lens bends the rays inward before they enter the eye, effectively adding to the eye lens's converging power so that the image now falls exactly on the retina.

Why the other options are wrong:

• (B) Diverging lens: A concave (diverging) lens is used to correct myopia (near-sightedness), which occurs when the eyeball is elongated or the eye lens is too curved, causing the image to form in front of the retina. This is the opposite defect.
• (C) Bifocal lens: Bifocal lenses (having both concave and convex portions) are prescribed for presbyopia, a condition arising from age-related weakening of the ciliary muscles where a person suffers from both myopia and hypermetropia simultaneously. The question describes a purely structural cause (reduced eyeball size), not an age-related combined defect.
• (D) Cylindrical lens: Cylindrical lenses correct astigmatism, a defect caused by an irregular (non-spherical) curvature of the cornea, which is not discussed in this chapter and is unrelated to eyeball size.