OD and OS are two of the most common abbreviations on an eyeglass prescription. They look technical, but the meaning is simple: OD identifies the right eye, and OS identifies the left eye. The labels help the lab make each lens for the correct side.
This guide explains what OD, OS, and OU mean, how they relate to SPH, CYL, AXIS, ADD, and PD, and what to check before entering your prescription online.
What Do OD and OS Mean?
OD stands for oculus dexter, the Latin term for right eye. OS stands for oculus sinister, the Latin term for left eye. Some prescriptions also use OU, which means both eyes.
Many eye doctors still use these abbreviations because they are short, standardized, and widely recognized by optical labs. You may also see plain English labels such as Right Eye and Left Eye on newer prescription forms.
| Term | Meaning | Where it matters |
|---|---|---|
| OD | Right eye | Right lens prescription values |
| OS | Left eye | Left lens prescription values |
| OU | Both eyes | Shared values that apply to both eyes |
Why OD vs OS Matters When Ordering Glasses
Many people have different values for the right and left eye. If OD and OS are swapped during online ordering, the lenses may feel blurry, uncomfortable, or hard to adapt to. This is especially important when one eye has stronger SPH, astigmatism, or a different AXIS value.
Before placing an order, compare the prescription form with the entry fields one row at a time. Do not rely on memory if your right and left eye numbers look similar.
How OD and OS Work With SPH, CYL, and AXIS
OD and OS are not the prescription power themselves. They are labels that organize the numbers for each eye.
| Field | What it means | Common note |
|---|---|---|
| SPH | Sphere power for nearsightedness or farsightedness | Negative values usually mean nearsightedness; positive values usually mean farsightedness |
| CYL | Cylinder power for astigmatism | May be blank if there is no astigmatism correction |
| AXIS | Astigmatism orientation | Usually a number from 1 to 180 |
| ADD | Extra near power | Often used for reading, bifocal, or progressive lenses |
| PD | Pupillary distance | Used to center lenses in the frame |
Example Prescription
A prescription might show OD: SPH -2.00, CYL -0.50, AXIS 180 and OS: SPH -1.75, CYL -0.25, AXIS 160. That means the right eye needs slightly different correction from the left eye, and each lens must be made separately.
If your prescription includes ADD, it may apply to both eyes or be listed separately. If your prescription includes PRISM, follow your eye-care provider's written values carefully because prism correction is more specialized.
Online Ordering Checklist
- Confirm whether the form uses OD/OS or Right/Left labels.
- Enter SPH for each eye exactly as written, including plus or minus signs.
- Enter CYL and AXIS together if astigmatism correction is present.
- Enter ADD only when you are ordering reading, bifocal, or progressive lens options that require it.
- Use the correct PD value. Some prescriptions show one single PD; others show dual PD for right and left.
- Review the final prescription summary before checkout.
For more help, read the PD guide and the eyeglass prescription guide.
FAQ
Is OD right or left eye?
OD means right eye. OS means left eye.
What does OU mean on an eye prescription?
OU means both eyes. It is used when a value applies to both eyes rather than being listed separately under OD and OS.
What happens if I switch OD and OS?
If your two eyes have different values, switching OD and OS can make the lenses feel wrong. You may notice blur, strain, headaches, or difficulty adapting.
Can I use my contact lens prescription for glasses?
No. Contact lens prescriptions and glasses prescriptions are different because contacts sit directly on the eye while glasses sit in front of the face. Use a current eyeglass prescription when ordering glasses.
Conclusion
OD and OS simply tell you which values belong to the right and left eye. Once those labels are clear, the rest of the prescription becomes easier to enter correctly. Take a minute to check OD, OS, SPH, CYL, AXIS, ADD, and PD before ordering glasses online.