Your prescription is written in a standardized clinical shorthand — here's what every piece of it means
An eyeglass prescription describes the optical correction your eyes need, broken into a handful of measurements. The main columns are OD (right eye, from the Latin oculus dexter) and OS (left eye, oculus sinister). Sometimes you'll see OU, which means both eyes together. The rows under those headings typically include SPH, CYL, Axis, and sometimes ADD and PD — each one capturing a different aspect of how your eye focuses light.
SPH (sphere) is the big one: it's the core correction power for nearsightedness or farsightedness, measured in diopters. A negative number (like −2.50) means you're nearsighted — you see close things clearly but distant objects blur. A positive number (like +1.75) means farsighted — distant objects may be clearer than near ones, though farsightedness is more complicated than that simple description. CYL (cylinder) and Axis together describe astigmatism, which is when the cornea or lens is slightly oval rather than perfectly round, causing blur at certain angles. If CYL is blank or reads "0.00," you don't have significant astigmatism.
ADD is a second number that appears if you need bifocal or progressive lenses — it represents the extra magnification needed for close-up reading, typically for people over 40 experiencing presbyopia (the gradual stiffening of the eye's natural lens). PD, or pupillary distance, is the measurement in millimeters between the centers of your pupils, which tells the lab exactly where to position the optical center of each lens in your frames.
The confusion shows up in different ways depending on which part of the prescription trips you up
Eyeglass prescriptions can be puzzling for different reasons — pick whichever version of the problem matches yours.
Getting the prescription wrong doesn't just mean blurry vision — it can mean wasted money and real eye strain
If you misread your prescription when ordering glasses — transposing OD and OS, entering the wrong sign on a CYL value, or skipping the Axis entirely — you'll receive lenses that actively distort your vision rather than correct it. Wearing an incorrect prescription for even a few weeks can cause persistent headaches, eye fatigue, and nausea. The glasses won't just be unhelpful; they'll make things worse. Most online retailers have limited return windows, so a mistake can mean paying twice.
Studies published in Optometry and Vision Science have found that up to 47% of glasses ordered online contain clinically significant errors — and many of those errors originate from patients incorrectly transcribing their own prescriptions, not from lab mistakes. Understanding your prescription before you order is the single most effective way to avoid this.
There is a trusted solution for this.
We've put together a complete, field-by-field decoder for every element of an eyeglass prescription — plus guidance on PD measurement, what to do with an ADD number, and when to push back on your optometrist.
See the Trusted Solution →Free to read · Independently verified · Updated March 2026
What others have experienced
47 community experiences-
MK
I stared at my prescription for a good twenty minutes before I felt comfortable entering it online. The part that tripped me up was that the CYL value for my right eye was negative and the left was blank — I kept thinking I'd made a mistake because they were so different. Turns out one eye just doesn't have astigmatism. Wish my optometrist had explained that for thirty seconds before handing me the paper.
31 found this helpful -
DP
The PD thing caught me completely off guard. I went to order glasses on one of the big discount sites and it asked for pupillary distance — which wasn't anywhere on my prescription. Called the optometrist's office and they were almost annoyed that I asked for it, like I was trying to take business elsewhere. I ended up measuring it myself with a ruler and a mirror using a tutorial I found. Glasses came out fine, but it shouldn't be this hard.
44 found this helpful -
TL
I have an ADD number on my prescription for the first time at 43 and I honestly didn't know what it meant. I assumed bifocals and was dreading it. Once I actually read about what ADD means I realized I had options — progressive lenses that don't have a visible line, or just a separate pair of inexpensive readers for the desk. My eye doctor hadn't walked me through any of that. I went with progressives and it took about a week to adapt but I'm glad I understood the choice I was making.
38 found this helpful
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