The ADD number is the power required to correct reading vision. As we get older, presbyopia starts to set in which is the hardening of the lens. This is what causes us unable to properly accommodate and focus on small objects (such as letters) and requires the use of reading glasses. The ADD, normally written in positive (+) diopters. These values can be used to order over the counter reading glasses or, with EyeGlass Numbers or a prescription, can be used to order multifocal lenses.
- How it Works