Bifocals are two foci glasses, i.e. which have two sections – one section corrects for distant vision and another corrects for near vision. Such glasses are especially convenient for people who have presbyopia – a disorder when one's eyes cannot focus on different objects, both distant and close. As a rule, this is a disorder of aged people.

Benjamin Franklin, an American politician and scientist, invented bifocals approximately in 1760 mostly because he himself had presbyopia. After their invention Franklin sent a letter to one of his acquaintances, saying that he was very glad he had managed to make these spectacles, because now he could recognize far objects as well as proximal rather easily.