A pair of eyeglasses with two different lens powers in each lens, allowing the wearer to see clearly at different distances.
Plural of 'bifocal,' referring to the actual glasses. Benjamin Franklin popularized this technology in the 1780s, making it a staple of vision correction.
Bifocals changed aging—suddenly older people didn't have to accept blurred vision or carry around multiple pairs of glasses. It's a technology so successful that we forgot how revolutionary it was.
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