Understanding your glasses prescription

Have you ever wondered what all the numbers in your glasses prescription mean?

It's not (quite) nonsense!

OD/OS:

Right Eye/Left Eye

Sphere:

The overall strength of your prescription. Near-sighted patients will have a (-) sign, for far-sighted patients, a (+) sign.

Cylinder:

Your astigmatism correction. This controls how the power is distributed throughout the lens.

Axis:

The orientation of your astigmatism correction. Given in degrees between 1-180.

Add:

Your reading prescription power (added on top of the spherical power.

Prism:  

Rarely used, but can be important for patients with eye turns.