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 eye because of which a person cannot see nearby objects clearly. This defect occurs because of the loss of the power of accommodation of the eye. Presbyopia usually occurs in old age.
The two causes of this defect are as follows.
1. Weakening of the ciliary muscles in old age.
2. Reduction in the flexibility of the eye lens.

Presbyopia, which is a special kind of hypermetropia, can be corrected by using spectacles with convex lenses.