Question

My grandfather uses a bifocal lens in his spectacle. Explain why?

Answer 1

The power of accommodation of the eye usually decreases with aging. For most people, the near point gradually recedes away. They find it difficult to see nearby objects comfortably and distinctly without corrective eyeglasses. This defect is called Presbyopia. It arises due to the gradual weakening of the ciliary muscles and diminishing flexibility of the eye lens.

This defect is corrected using a bifocal lens whose upper portion consists of a concave lens that facilitates the distant vision and the lower part is a convex lens that facilitates near vision.