Your eyeglass prescription looks like a small spreadsheet of abbreviations and plus and minus signs. Once you know what each box means, it takes about a minute to read, and it's all you need to order prescription glasses online.
OD and OS: right eye and left eye
Prescriptions are written with one row per eye. The labels come from Latin:
- OD (oculus dexter) is your right eye.
- OS (oculus sinister) is your left eye.
- OU (oculus uterque) means both eyes. You'll sometimes see it next to a note that applies to both.
Some doctors simply write R and L. Same thing.
An example prescription
| Eye | SPH | CYL | Axis | ADD |
|---|---|---|---|---|
| OD | -2.25 | -0.75 | 180 | — |
| OS | -2.00 | -0.50 | 175 | — |
PD 63
Here's how to read each column.
SPH (sphere): your main lens power
Sphere is the main strength of the lens, measured in diopters, and it's written in steps of 0.25.
- A minus number (like -2.25) means you're nearsighted: distant things are blurry.
- A plus number (like +1.50) means you're farsighted: close-up things are harder to focus on.
- PL or Plano means 0.00, no correction in that eye.
The further the number is from zero, the stronger the prescription.
CYL (cylinder): correction for astigmatism
Cylinder corrects astigmatism, which happens when the front of your eye is shaped more like a football than a basketball. If the CYL box is blank, or says DS or SPH, you don't have astigmatism correction in that eye. When you order, choose 0.00.
CYL can be written with a minus sign or a plus sign depending on your doctor's convention. Both are correct. Just copy it exactly as written.
Axis: the direction of the cylinder
Axis is a number from 1 to 180 that tells the lab which direction to orient the cylinder. It only matters when there's a CYL value. It is not a strength, so a bigger number isn't "worse." An axis of 180 and an axis of 90 are simply different directions.
ADD: extra power for reading
ADD is extra magnifying power for close work, used in bifocal and progressive lenses. It's usually the same for both eyes and is often written once. We make single vision lenses, which have one power across the whole lens. If your prescription has an ADD, read single vision vs. bifocal vs. progressive and email us before ordering.
Prism
A small number of prescriptions include prism, with a base direction like "BO" (base out) or "BI" (base in), to help eyes that don't line up perfectly. Prism is less common. We can't fill prism prescriptions right now.
PD (pupillary distance)
PD is the distance between the centers of your pupils in millimeters. It tells the lab where to put the optical center of each lens. It isn't always written on the prescription, but you can measure your PD at home in a couple of minutes. You might see it as one number (63) or two (31.5/31.5).
Check the date
Most eyeglass prescriptions include an issue date and often an expiration date. See how long a prescription is good for. If your vision has changed, get a new eye exam before ordering.
Ready to order?
At checkout you can type your SPH, CYL and Axis for each eye plus your PD, or just upload a photo of your prescription. We'll double-check the numbers. Everyday frames are $79 and safety frames are $149, with single vision lenses included. Browse all frames.
