People are both nearsighted and farsighted wear bifocals. Bifocal eye glasses work by accommodating eyes that are both nearsighted, or myopic, and farsighted, or hyperopic. This means a person requiring both prescriptions is presbyopic. Bifocal vision means a person needs two separate prescriptions, one to see clearly at a distance and a different one to see up close.
When you can see distant objects with regular glasses, but you cannot read a book with that glasses, so you also need a pair of reading glasses help you focus on near objects. In this case, you need a pair of glasses that can meet your needs for both reading and viewing far. Then the bifocal glasses can suit your needs fine whose lenses are divided into two parts, the top part is for far and the bottom part is for near.
Bifocal glasses are usually needed by people over 40 who are nearsighted and have presbyopia at the same time.Due to the eye muscles degeneration as they old,their eyes lose the elasticity of seeing both near and far.So they need the bifocals to help correct their vision.