Bifocal lens is used for the correction of which of the following diseases?

Presbyopia

Sometimes, a person may suffer from both myopia and hypermetropia. This defect is called Presbyopia.

It arises due to the gradual weakening of the ciliary muscles and diminishing flexibility of the eye lens. 

Such people often require bi-focal lenses.

A common type of bi-focal lenses consists of both concave and convex lenses.

The upper portion consists of a concave lens. It facilitates distant vision.

The lower part is a convex lens. It facilitates near vision.