Sphere & Cylinder
Axis & Add
Full Glossary
Your Prescription, Term by Term
Sphere, cylinder, axis, add, PD -- a full glossary of every value that can appear on an eyeglass prescription.
| Term | What It Means |
|---|---|
| OD / OS | OD (oculus dexter) is your right eye; OS (oculus sinister) is your left eye. |
| SPHERE (SPH) | The main correction strength, in diopters. Negative = nearsighted, positive = farsighted. |
| CYLINDER (CYL) | The strength of astigmatism correction, if you have astigmatism. Blank means none. |
| AXIS | The orientation (1-180 degrees) of your astigmatism correction. Only appears alongside CYL. |
| ADD | Extra magnifying power for close-up focus, used in bifocal and progressive lenses for presbyopia. |
| PD | Pupillary distance -- the distance between your pupils in millimeters, used to center your lenses. |
| PRISM | A less common value correcting eye alignment issues, prescribed for specific conditions. |
Putting It Together
A full prescription line might read: OD -2.25 -0.75 x 180, ADD +1.50. That translates to: right eye, moderate nearsightedness (-2.25 sphere), mild astigmatism (-0.75 cylinder) oriented at 180 degrees, plus a +1.50 add power for close-up focus if you need progressive or bifocal lenses.
PD is sometimes listed on the prescription and sometimes measured separately at checkout -- see our PD measurement guide if yours isn't included.
Frequently Asked Questions
Why are there two rows on my prescription? +
One row for each eye -- OD for right, OS for left. It's common for the two eyes to have slightly different prescriptions.
What if my PD isn't on my prescription? +
PD is often measured separately since many eye doctors don't include it by default. You can measure it yourself using our PD measurement tool or guide.
Is a negative or positive sphere number worse? +
Neither is 'worse' -- negative indicates nearsightedness (myopia) and positive indicates farsightedness (hyperopia). The number's size indicates strength, not severity in a good/bad sense.
What does it mean if CYL and AXIS are blank? +
It means you don't have a meaningful degree of astigmatism, and your lenses only need the sphere correction.
More Helpful Guides
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