What Does the ADD Number Mean on Your Glasses Prescription?

When you look at your glasses prescription, you may see familiar headings such as SPH, CYL and AXIS.

But some prescriptions also contain another value: ADD.

So what does ADD mean, and why doesn't everybody have one?

What does ADD mean?

ADD is short for addition.

It represents additional plus power prescribed to help with near vision.

Rather than replacing your distance prescription, the ADD value is used alongside it when calculating the power required for closer tasks.

Why might you need an ADD?

As we get older, the natural lens inside the eye gradually becomes less flexible.

This makes it harder for the eyes to focus comfortably on objects at close distances.

This age-related change is called presbyopia and commonly becomes noticeable from around the age of 40 onwards.

An ADD may therefore be prescribed to provide additional focusing power for near vision.

What does an ADD look like on a prescription?

You may see a value such as:

ADD +1.50

The exact number varies depending on the amount of additional near power required.

Unlike CYL and AXIS, an ADD isn't describing astigmatism.

Is ADD the same for both eyes?

Often the same ADD is prescribed for both eyes, although your full spectacle prescription should always be followed exactly as written.

Never assume that a value applies to both eyes unless this is clear from your prescription.

Does having an ADD mean you need reading glasses?

An ADD can be used when determining a prescription for near-vision glasses.

For example, somebody who already has a distance prescription may require additional power when their glasses are intended specifically for reading or other close work.

The final near prescription depends on both the underlying prescription and the ADD.

Is ADD the same as your reading prescription?

Not exactly.

The ADD is the additional power required for near vision.

It isn't necessarily the complete lens power that would be placed into a pair of reading glasses.

Your existing prescription needs to be taken into account as well.

Why isn't there an ADD on my prescription?

Not everybody requires additional near-vision power.

Younger people can generally change the focus of their eyes naturally when looking from distance to near.

If additional near correction isn't required, there may simply be no ADD value on the prescription.

Can the ADD change over time?

Yes.

As the eye's natural focusing ability changes with age, the amount of additional near power required can also change.

This is one reason why having regular eye examinations remains important rather than relying indefinitely on an old prescription.

Don't enter an ADD where it isn't requested

When ordering glasses online, pay attention to exactly what information is being requested for the type of lenses you're buying.

Don't copy numbers into unrelated fields simply because they appear on your prescription.

If you're uncertain about what a particular value means, check before placing the order.

Another part of the prescription made simpler

ADD can initially look like another confusing abbreviation, but its purpose is straightforward.

It represents the extra lens power prescribed for near vision.

Once you understand that distinction, reading the different sections of your spectacle prescription becomes considerably easier.