What does the term 'addition' mean in relation to multifocal lenses?

The term 'addition' in relation to multifocal lenses specifically refers to the difference in plus power between the reading portion and the distance portion of the lens. Multifocal lenses, such as bifocals or progressive lenses, are designed to assist individuals who require different optical powers for various distances.

In a multifocal lens, the distance portion is typically designed for seeing objects that are far away, while the addition is the extra power that allows for clear vision at closer distances, such as reading. This added power is essential for those with presbyopia, a common condition that affects the ability to focus on close objects as people age. Therefore, understanding the 'addition' is crucial for ensuring that the lenses are tailored to provide the necessary support for both distance and near vision.