A progressive lens in front of ruled paper, the lines appearing larger through its lower part.

Reading a prescription

Addition (ADD)

Optical glossaryReading a prescription

The extra reading power added to the lower part of a progressive or bifocal. Typically starts near +1.00 in the early forties and usually settles near +2.50 (up to +3.00 for close working distances).

The addition is written once and usually matches for both eyes. Added to the sphere, it gives the reading power in the lower part of the lens.

Illustrative · the shape of the principle, not measured data

In more depth

The addition, written ADD, is extra plus power for close work, stacked on top of the distance prescription. It is written once and is usually the same for both eyes. Your reading power is the sphere plus the addition: a −1.00 distance prescription with a +2.00 addition reads at +1.00.

It rises with age as the eye's own focusing declines. In a progressive lens the addition is reached gradually down the corridor, and the intermediate zone carries part of it — which is what makes a screen at arm's length comfortable, and what a bifocal, with nothing between its two zones, cannot offer.

Worked example

Distance
−1.00
Addition
+2.00
Reading power
+1.00

Related terms

PresbyopiaThe age-related stiffening of the eye's internal lens that makes close focus difficult, typically from the early forties. Not a disease — the reason reading additions and progressives exist.Progressive lensA lens whose power changes gradually from distance at the top to reading at the bottom, with no visible line.CorridorThe channel of clear vision running down the center of a progressive, connecting the distance and reading zones.BifocalA lens with two distinct zones separated by a visible line, and no intermediate correction between them.

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