What does bifocal mean?
Bifocal describes a lens that combines two different corrective powers within a single piece of glass or plastic — typically an upper portion ground for viewing distant objects and a lower portion suited to close work such as reading. The word most often appears as an adjective before nouns like 'bifocal glasses' or 'bifocal lenses', but it also functions as a noun, nearly always in the plural form 'bifocals', meaning a pair of eyeglasses made with such lenses. Bifocals are strongly associated with presbyopia, the age-related stiffening of the eye's focusing mechanism that usually begins in middle age, which gives the word a quiet association with growing older — hence its occasional humorous use in jokes about midlife. The two zones of a traditional bifocal are divided by a visible line, distinguishing them from modern progressive ('varifocal') lenses, which blend powers gradually without any seam. First popularized in the late eighteenth century and long credited to Benjamin Franklin, bifocals remain a practical and familiar solution for people who need help seeing both far and near.
(Of a lens) having two regions with different refractive powers, one for distance vision and one for near tasks such as reading.
"Her new bifocal spectacles let her watch television and read her book without changing pairs of glasses."
Almost always used attributively, immediately before a noun like 'glasses', 'lenses', or 'spectacles'.
Usually in the plural form 'bifocals': a pair of eyeglasses fitted with lenses that have two different optical powers.
"Since turning fifty, my father has refused to be seen in public without his bifocals."
Virtually always plural; the singular 'a bifocal' is uncommon and generally refers to a single lens rather than a pair of glasses.
When used as a noun, 'bifocal' conventionally takes the plural form 'bifocals' to refer to a whole pair of glasses, treating the object as a single item despite the plural ending.
"She bought a new pair of bifocals after struggling to thread a needle with her old prescription."
Benjamin Franklin is widely credited with inventing bifocals in the 1780s — reportedly because he was tired of switching between two pairs of glasses just to read and then look around.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of bifocal
Bifocal derives from the Latin prefix bi-, meaning 'two', combined with focal, from Latin focus, meaning 'hearth' or 'fireplace', which in optics came to denote the point where light rays converge. The compound was formed in English in the late eighteenth century, at the same time the invention itself emerged. The word shares its root with related terms such as focus, focal, and focalize, all tracing back to that same Latin noun.
Related word forms
How bifocal is actually used
As an adjective, 'bifocal' normally modifies 'glasses', 'lenses', or 'spectacles'. As a noun it almost always appears in the plural form 'bifocals'; the singular 'bifocal' referring to one lens or pair is rare. The word is neutral in register and common in both everyday and optometric contexts. In British English, 'bifocals' is standard, though 'bifocal spectacles' may also be heard.
Easily confused with bifocal
Bifocal lenses have exactly two distinct zones of power separated by a visible line, while varifocal (progressive) lenses change power gradually across the lens with no dividing line.