Question

Which lens is used to correct the defect of vision formed as Presbyopia.

Answer 1

Hint: We can see what the defect of Presbyopia is, then accordingly with which suitable lens amongst concave, convex or both can be used for its correction.
Due to this, people are not able to see the objects clearly placed near them. This is known as the defect of Presbyopia.
Complete step by step answer:
As we grow older, due to ageing, the muscles of the eyes (ciliary muscles) become weak and the flexibility of the eye lens decreases.
Correction:
Bi – focal lenses are used to correct the defect of Presbyopia. As Presbyopia occurs with age, the person might suffer difficulty in seeing objects both near and farther as the power of accommodation is lost.

The person having this defect might suffer from both myopia and hypermetropia.
Myopia is the defect of short sightedness, the person can clearly see the objects near him but not the farther ones. So, it is corrected by using a concave lens of suitable power to see distant objects.
Hypermetropia is the defect of long sightedness, the person can clearly see the objects farther from him but not the nearer ones. So, it is corrected by using a convex lens of suitable power to see the nearby objects.
Therefore, for the correction of Presbyopia, bi – focal lens whose upper portion is made up of concave and lower of convex lens.

Note:
A convex lens can also be used for treating the defect of presbyopia, but as it is due to the weakening of muscles because of ageing, bi-focal lens is mostly preferred.
Presbyopia is also called as the special case of the defect called hypermetropia (long sightedness)