What Do Your Eye Prescription Numbers Mean?

Ever looked at your eye prescription and thought, “What does any of this even mean?” You’re not alone — all those numbers and abbreviations can feel like a secret code.

The good news? It’s actually not that complicated once you know what each part stands for.

In this guide, we’ll break down all those terms — SPH, CYL, Axis, ADD, and more — in plain, simple language so it all makes sense.

You’ll usually see a table that looks something like this:

OD and OS – Which Eye is Which?

• OD = Right Eye
• OS = Left Eye

They’re just short for some fancy Latin terms: Oculus Dexter and Oculus Sinister.

SPH (Sphere) – Nearsighted or Farsighted?

This one tells you if you’re short- or long-sighted:

• A minus (-) sign = you’re nearsighted (you see better up close).
• A plus (+) sign = you’re farsighted (you see better far away).

The bigger the number, the stronger your lens needs to be.

CYL (Cylinder) – Do You Have Astigmatism?

This part is all about astigmatism, which just means your eyeball isn’t perfectly round (totally normal, by the way).

• If there’s a number here, you’ve got astigmatism.
• If it’s blank, your eyes are pretty round and don’t need correction for that.

AXIS – Direction of Astigmatism

If you’ve got a number under CYL, you’ll also see an AXIS number — usually between 0 and 180. This tells us where to place the correction in your lens.

Don’t worry about this one too much. It’s more for the people making your glasses than for you to memorise.

ADD – Extra Power for Reading

If you’re over 40 or experiencing difficulty seeing things up close, your prescription may include an ADD value. This is an extra boost for reading or close-up work, commonly used in multifocal or progressive lenses.

PD – Pupillary Distance

This is the distance between your pupils — super important for making sure the lenses line up with your eyes properly. Even a small misalignment can mess with your vision, so it’s worth getting it right.