Presbyopia is a condition in which the normally soft, flexible lens becomes hard and resistant to changes in shape. As a result, the eye has difficulty focusing when looking at close objects and reading vision becomes blurred and difficult.

Presbyopia normally occurs about the age of 40. There is no way to prevent presbyopia, as this loss of focusing ability is a normal part of the aging process. Bifocals and reading glasses, which aid the eye in focusing close objects, are used to treat presbyopia.