Bifocal spectacles are eyeglasses that have lenses with two different corrective powers. The spelling of "bifocal" includes the use of the "i" after "b," indicating the pronunciation of the letter "i" as /aɪ/. The word "spectacles" includes the letter combination of "ct," which is pronounced as /kt/ in IPA phonetic transcription. Overall, the spelling of "bifocal spectacles" accurately depicts the pronunciation of the word and allows for clear communication about this type of eyewear.
Bifocal spectacles refer to a type of eyeglasses designed to correct both near and distant vision problems. They consist of lenses divided into two distinct optical sections, each having a different refractive power. The upper part of the lens caters to correcting distance vision, while the lower part is specifically designed for near vision correction.
The purpose of bifocal spectacles is to alleviate presbyopia, an age-related condition where the eye's ability to focus on objects up close gradually weakens. Presbyopia typically affects individuals around or after the age of 40, making it difficult for them to see things clearly at close range. By incorporating two powers in a single lens, bifocal spectacles enable wearers to have clear vision at both near and far distances without switching between different pairs of glasses.
The lower half of the lens, meant for close-up vision correction, is usually distinguished by a visible, semi-circular segment known as a "bifocal segment" or "add power." This add power provides extra magnification required for reading or other activities done at a short distance. The top portion of the lens, for distance vision, typically remains unaltered. Bifocal spectacles are available with different segment designs including flat-top, round-segment, and executive styles, allowing wearers to choose the most suitable design based on their specific visual needs and aesthetic preferences.
Overall, bifocal spectacles offer a convenient and efficient solution for individuals experiencing both near and distance vision problems, allowing them to enjoy improved visual clarity and quality across different ranges.
See bifocal.
A practical medical dictionary. By Stedman, Thomas Lathrop. Published 1920.
The word "bifocal" is derived from two Latin roots: "bi-" meaning "two" and "focus" meaning "a point at which rays of light meet after passing through a lens". The term "spectacles" on the other hand, comes from the Latin word "spectaculum", meaning "a sight" or "a spectacle". Therefore, the etymology of the term "bifocal spectacles" essentially combines the concept of lenses with two different focal lengths, allowing individuals to see objects at different distances.