what are bifocal glasses

Bifocal glasses 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 two different prescriptions are separated by a visible line on the lens. Bifocal glasses 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 first bifocal was invented by Benjamin Franklin, who glued the top half of one lens to the bottom half of another. Modern bifocal lenses have evolved from this simple design and include flat-top bifocals, round segment bifocals, and narrow rectangular ribbon segment bifocals. Bifocal glasses are not the only option for people with presbyopia, as there are also progressive lenses that provide a seamless no-line lens design and clear vision at distance, intermediate, and near.