Bifocals

• Bifocals are eyeglasses, invented by Benjamin Franklin, which are formed from two different types of lenses. Typically, the upper lens corrects for distance, and the lower lens corrects for near vision, such as reading or computer work. Today's technology has allowed for bifocals to combine both types of lenses seamlessly into one frame.
  
  

Near Vision Correction

• Found on the lower part of the glasses, the near vision lens is a convex piece of glass or plastic which can be one of four types: half-moon, round, rectangular or half cut. When reading something close in proximity, an individual would look down through the near vision part of the bifocals. This part of the lens is more convex than the portion for distance viewing.
  
  

Far Vision Correction

• When focusing on objects further away, the bifocal wearer looks up and through the distance correction portion of the lens. This is the least convex part of the lens. Occasionally, there may be no correction needed in this part of the lens, for those who do not have trouble viewing objects from a distance but do, however, need vision correction for nearby objects.
  
  

Lenses

• Bifocals can be made by fusing together two separate types of lenses, or by using one piece of glass or plastic which contains different curvatures on its surface. Sometimes, bifocals can cause headaches and/or dizziness due to the adjustments necessary for the eyes when looking through either part of the lens.