what is add on eye prescription

An ADD eye prescription refers to the additional lens power required to help your eyes focus for reading, and is added to the sphere prescription for individuals who require assistance with near vision due to presbyopia. The number appearing in the prescription is always a plus power, even if without a plus sign (+) . The ADD value is usually the same for both eyes, but on certain rare occasions, it could be different between the two eyes. The ADD value is the amount of magnification required to "ADD" to the "SPH" value of your "Distance" prescription to correct your near vision. The ADD value may be written in the "Near Addition" space on your prescription, but it can also be written somewhere under or next to the distance values. The ADD value applies to both eyes and can sometimes be written only once on the prescription, even though the addition is required for both eyes. If you have a prescription for reading glasses or the lower portion of bifocal or progressive lenses, you will see an ADD value on your prescription.