what are bifocal lenses

Bifocal lenses are a type of eyeglasses that feature two different optical powers in one lens. The top part of the lens corrects distance vision, while a smaller portion at the bottom of the lens corrects near vision. The lens segment devoted to near-vision correction can be one of several shapes, including a half-moon, a round segment, or a narrow rectangular area. When looking closely at bifocal lenses, you can see a line where these different viewing zones meet. Bifocal lenses are commonly used to help the eye adjust vision to focus on objects that are close once it begins to lose the ability to transition focus due to age-related conditions like presbyopia. The most modern bifocal lenses are called “No-line” or “Progressive” lenses, which have a smooth change in focus from the top of the lens (distance), through the middle (arm’s length), to the bottom of the lens (reading distance) .