What it means and why
ADD is extra plus power relative to the distance spherical component for a specified near or intermediate task. It is a difference between two requirements, not necessarily the complete reading power printed on a ready-made reader.
The task matters: a phone, book and monitor are often at different distances. The examiner considers working distance and the person’s remaining focusing ability. Age alone does not supply all those inputs.
A worked example
Teaching arithmetic: distance SPH −3.00 D with ADD +1.50 D gives a near spherical component of −1.50 D in a straightforward prescription example. Any cylinder, axis or prism still needs to be preserved as prescribed. This explains the notation and is not a way to prescribe your own readers.
What it does not tell you
Do not add ADD to CYL or treat it as a uniform extra power across a whole progressive lens. The progressive distributes the distance-to-near change spatially.
THINK IT THROUGHDoes ADD +1.50 mean every wearer needs +1.50 readers?
No. The distance prescription and task are part of the calculation; ADD is only the additional component.
Sources & reading notes
Page updated:
- ABDO · Explaining spectacle prescriptions, part 2 ↗ Professional body guidance
Explains terminology and dispensing practice; it is not a head-to-head product trial.