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

In the context of a bifocal prescription, the term used to refer to the reading portion is "Addition." This refers specifically to the additional power added to the distance vision prescription to allow for near vision tasks, which is essential for activities such as reading.

Bifocal lenses are designed to provide both distance and near vision correction, and the "Addition" indicates how much extra magnifying power is required for viewing objects that are close up. This measurement is crucial for individuals who have presbyopia, a common age-related vision condition that makes it difficult to focus on nearby objects.

The other terms—Sphere, Cylinder, and Axis—refer to different aspects of a prescription. "Sphere" indicates the degree of nearsightedness or farsightedness, "Cylinder" is related to astigmatism, and "Axis" denotes the orientation of astigmatism correction. While these elements are important for a comprehensive understanding of a prescription, they do not pertain specifically to the reading portion of bifocals.