What is the term for the reading portion of a bifocal prescription?

The term for the reading portion of a bifocal prescription is known as the "Addition." This term refers to the additional lens power that is incorporated into the lower part of the bifocal lens to assist with near vision tasks, such as reading. In bifocal lenses, the upper portion is typically designed for distance vision, and the lower portion, or the addition, is intended to provide the necessary magnification for close-up work.

Understanding this term is important for anyone involved in optometry or the fitting of glasses, as it indicates how much extra power is added to the lens for near vision. This designation helps ensure that individuals with presbyopia, a common age-related vision change, receive the appropriate correction for their specific reading needs.