Bifocal glasses, as the name implies, provide two different types of lens powers. They are commonly used by people who have presbyopia, a condition that often affects people over age 40. At that point, the lens of the eye is losing elasticity, and you begin to lose the ability to focus on objects that are near to you. You may find yourself holding the newspaper farther and farther away in order to focus on the type, while objects at a distance remain in relatively clear focus. Bifocals let you see both near and far clearly, by using different areas of the lens for each type of focus. Bifocals are also used for children or younger adults to alleviate chronic eye strain or issues with focusing, particularly for reading. They are also sometimes used to treat myopia or nearsightedness in children.