One type of bifocal contact lens is designed to have both the distance and near portions within the pupil at the same time. These are called simultaneous vision lenses.
These lenses produce a clear image
with an overlying blurred image. If
the patient is viewing a distance
object, the image through the distance
portion is clear while that through the
near portion will be out of focus. The
patient must pay attention to the clear
image and ignore the blurred one.
Some simultaneous vision lenses have the distance portion in the center while others have the near portion in the center.
Lenses with one zone surrounding the other in this fashion are called concentric designs.
