The eye is able to change focus, sometimes seeing objects that are close and sometimes seeing objects that are far away. 

This is made possible by a flexible lens inside the eye that can change shape depending on the distance of the object that is seen. As the eye ages, this lens becomes less flexible and loses its ability to focus on close objects; this condition is called Presbyopia.

This change in the eye is natural and happens to everyone, usually becoming noticeable in the early to mid 40s.  Presbyopia is not a disease and it cannot be prevented or treated, but it is easily corrected for with contact lenses.

A contact lens for presbyopia will generally have two optical portions, one that focuses on near objects and one that can focus on distant objects.  If there is a distinct junction between these areas, the lens is called a bifocal.

If the near focus portion of the lens transitions smoothly into the distance portion, the lens is called a multifocal.  There are many different types of lenses designed to treat presbyopia, your eye care professional can help you find the one that works best for you.