An eyeglass prescription can look like a confusing mix of numbers and abbreviations, but each part tells us something specific about how your lenses should be made.
Here’s a simple breakdown.
OD & OS
These identify each eye:
OD = Right eye
OS = Left eye
You may also see OU, which means both eyes.
SPH — Sphere
Sphere tells us the main amount of vision correction needed.
- A minus (-) number typically corrects nearsightedness.
- A plus (+) number typically corrects farsightedness.
The farther the number is from zero, the stronger the prescription.
CYL — Cylinder
Cylinder measures the amount of astigmatism correction needed.
Not everyone has a CYL value. If you do, it works together with the Axis measurement.
AXIS
Axis tells us the orientation of the astigmatism correction.
It is measured from 1 to 180 degrees.
The Axis does not tell us how strong your prescription is—it simply tells us where the cylinder correction needs to be positioned.
ADD
ADD is used when additional magnification is needed for near vision.
You’ll commonly see this on prescriptions for:
- Progressive lenses
- Bifocals
- Reading glasses
PD — Pupillary Distance
PD stands for Pupillary Distance.
It measures the distance between your pupils and helps us position the optical centers of your lenses correctly in front of your eyes.
A good PD measurement is important for comfortable, accurate vision—especially with stronger prescriptions and progressive lenses.
Why Accurate Measurements Matter
Your prescription tells us what correction you need, but proper eyewear also depends on how that prescription is positioned in the frame.
Frame size, PD, fitting height, lens design, and other measurements can all influence how your finished glasses perform.
The Bottom Line
Your eyeglass prescription is more than a list of numbers.
Each measurement helps determine how your lenses should be designed and positioned so your glasses provide the vision correction intended by your eye-care professional.
At Yay Optics, our goal is to make ordering prescription eyewear easier to understand—without oversimplifying the details that matter.