What Your Eyeglasses Prescription Really Means

You’ve just had an eye exam, and the optometrist hands you a slip of paper filled with mysterious numbers, plus and minus signs, and abbreviations. You know it’s your eyeglasses prescription—but what do all those codes actually mean? Let’s break it down so you can understand exactly what’s on that piece of paper.



The Basics: OD and OS

  • OD: Latin for oculus dexter, meaning “right eye.”

  • OS: Latin for oculus sinister, meaning “left eye.”
    Some prescriptions may also show OU (oculus uterque), which means “both eyes.”

These abbreviations simply tell you which measurements belong to which eye.

Sphere (SPH)

The sphere value corrects nearsightedness or farsightedness.

  • A minus (-) sign means you’re nearsighted—you see better up close than far away.

  • A plus (+) sign means you’re farsighted—you see better far away than up close.

The higher the number, the stronger the prescription. For example, -1.50 is mild, while -5.00 is considered strong.

Cylinder (CYL) and Axis

If your prescription lists a CYL number, you have astigmatism, which means your cornea is shaped more like a football than a basketball.

  • CYL: Indicates the amount of correction needed.

  • Axis: A number between 1 and 180 that tells the lab exactly where to position that correction.

Add

This is the “added” magnifying power for reading and close-up work—usually for people with presbyopia, a normal age-related change in near vision. You’ll see this in bifocal or progressive lens prescriptions.

PD (Pupillary Distance)

PD measures the space between your pupils in millimeters. This is crucial for making sure your lenses are perfectly centered with your eyes for clear, comfortable vision.

Prism

Not as common, prism correction helps align your eyes to correct double vision or other focusing issues.

Putting It All Together

A prescription might look like this:

EyeSPHCYLAxisAddOD-2.00-0.7590+2.00OS-1.50-0.5085+2.00

This tells the optical lab:

  • Right eye: moderate nearsightedness, mild astigmatism at 90°, plus reading power.

  • Left eye

Jenna Offerdahl