Bifocal glasses
Bifocal glasses are a type of eyewear designed to correct presbyopia, a condition that typically affects individuals over the age of 40. The term "bifocal" is derived from the Latin words "bi", meaning two, and "focal", meaning focus.
Pronunciation
The term "bifocal glasses" is pronounced as bi·fo·cal glasses.
Etymology
The term "bifocal" was first used in the late 18th century and is derived from the Latin "bi-", meaning "two", and "focal", referring to the two different optical powers these glasses possess.
Description
Bifocal glasses have two distinct optical powers. The upper part of the lens is used for distance vision, while the lower part is used for near vision. This design allows the wearer to switch between distant and near vision by simply moving their eyes up or down.
Related Terms
- Presbyopia: A condition that affects the eye's ability to focus on close objects. It typically occurs as part of the aging process.
- Eyeglasses: A device consisting of glass or hard plastic lenses mounted in a frame that holds them in front of a person's eyes.
- Optical power: The degree to which a lens magnifies the vision of the eye.
- Lens (optics): A piece of glass or other transparent substance with curved sides for concentrating or disseminating light rays.
History
The invention of bifocal glasses is often attributed to Benjamin Franklin, who is believed to have developed them in the 1780s to correct his own vision problems. However, some sources suggest that bifocals may have been in use earlier.
See Also
External links
- Medical encyclopedia article on Bifocal glasses
- Wikipedia's article - Bifocal glasses
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