What is presbyopia? Write two causes of this defect. Name the type of lens which can be used to correct presbyopia.

Presbyopia is a defect of the vision due to which a person cannot see nearby objects clearly (appears blurred) due to the loss of power of accommodation of the eye. It usually occurs in old age.

The two causes of this defect are as follows:

1. Weakening of the ciliary muscles in old age.

2. Diminishing flexibility of the eye lens.

It is also known as a special kind of hypermetropia, and it can be corrected by using convex lenses.