Bifocal contact lenses are worn by patients suffering from presbyopia, a condition that occurs around the age of forty and is usually signaled by the inability to read print that is too close, such as a menu or book. Patients suffering from presbyopia find themselves holding reading materials at arms length to focus on them.
Presbyopia is believed to be caused by the continuing loss of flexibility in the natural lens inside your eye as you age. This occurs within the proteins of the lens. The lens in your eye becomes harder and loses elasticity, making it difficult to focus on objects up close.
Bifocal contact lenses correct presbyopia by having two powers in one lens. One part of the lens corrects distance vision and the other corrects near vision. There are a few different types of designs used to create bifocal contacts.
An Aspheric design changes powers gradually, from the center of the lens to the edge. Gradual change in lens power allows for intermediate distance correction.
A concentric design utilizes the center of the lens for one power and the outside of the lens for the other.
A translating design has the near vision correction on the bottom and the far vision correction on the top. To keep the lens from rotating when you blink, the bottom edge of the lens is flat.
Bifocal lenses are manufactured as both soft and gas permeable lenses. Since 1999, disposable bifocal contacts have been available for purchase, including daily disposables.