CBSE Class 10 Science 2020 · Paper 31/2/3 · Question 23(a)

The three common refractive defects of vision and their correction: (i) Myopia (near-sightedness): distant objects are not seen clearly because their image forms in front of the retina. It is corrected by a concave (diverging) lens of suitable power. (ii) Hypermetropia (far-sightedness): nearby objects are not seen clearly because light from them would focus behind the retina. It is corrected by a convex (converging) lens of suitable power. (iii) Presbyopia: with age the power of accommodation decreases and the near point recedes. It is corrected by bi-focal lenses, with a concave upper part for distant vision and a convex lower part for near vision (a convex lens alone where only near vision is affected). These defects can also be corrected with contact lenses or by surgery.