A person is wearing spectacles which is (i) thicker at the centre (ii) thinner at the centre and (iii) made of two different types of lenses. Identify the type of lens and the defect of vision the person is suffering from, in each case.

Explanation

(i) The lens is convex and the defect of vision is hypermetropia.
(ii) The lens is concave and the defect of vision is myopia. (iii) The lens is bifocal and the defect of vision is presbyopia.