How to read your eyeglass prescription before buying glasses online
Decode OD/OS, SPH, CYL, AXIS, ADD and PD so you can enter your prescription correctly at any online glasses retailer, plus where to buy by need.
Buying glasses online is dramatically cheaper than at a clinic counter — but at checkout you hit a wall of abbreviations: OD, OS, SPH, CYL, AXIS, ADD, PD. Enter them wrong and your glasses arrive blurry and, depending on the retailer, non-refundable for a "user-error" mistake. This guide decodes every line of a standard U.S. eyeglass prescription so a first-timer can confidently enter their numbers at an online retailer.
It is written from a research stance — based on how optical prescriptions are standardly formatted and how the major online retailers structure their order forms per their published help pages, not a clinical exam. It is general consumer-shopping information, not medical or optometric advice. LensVerdict is not an eye-care provider. Always get an eye exam and a valid prescription from a licensed optometrist or ophthalmologist, and have any contact-lens fit set by your eye doctor.
Affiliate disclosure: LensVerdict earns a commission via Commission Junction (CJ) when you buy through some of our links, at no extra cost to you. Commissions never change our recommendations — our retailer picks are based on price, lens range, return policy, and how easy each site makes entering a prescription. The retailer links below are pending CJ program approval, so treat them as "where to compare and apply," not live deals.
First: where to get your prescription
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You cannot legally buy prescription lenses online without a valid prescription. In the U.S., the FTC's Eyeglass Rule requires your eye doctor to give you a copy after a refraction, whether or not you ask — so you are entitled to the numbers. Two things to confirm before you shop:
- Your prescription is current. Most are valid for one to two years, and many retailers ask you to confirm it is unexpired. An expired script means a new exam, not a workaround.
- You have an eyeglass prescription, not a contact-lens prescription. A contact-lens prescription includes base curve and diameter and is brand-specific; it will not work for glasses. If you only have contacts numbers, request the eyeglass version.
The layout: OD vs OS (and "OU")
Every prescription is organized into rows, one per eye. The abbreviations are Latin:
- OD (oculus dexter) = your right eye.
- OS (oculus sinister) = your left eye.
- OU (oculus uterque) = both eyes (used when the values are identical).
Some modern prescriptions skip the Latin and simply write "Right" and "Left." Either way, match each row to the correct eye in the form. Order forms label the fields OD/Right and OS/Left, and transposing them is one of the most common and most preventable mistakes.
Decoding each column
Here is what each standard field means and what you type at checkout.
| Field on your Rx | What it means | What to enter online |
|---|---|---|
| SPH (Sphere) | Power for nearsightedness (minus, e.g. -2.50) or farsightedness (plus, e.g. +1.75), in diopters | The exact number with its + or - sign. "Plano," "PL," or "0.00" means no spherical correction. |
| CYL (Cylinder) | The amount of astigmatism correction, if any | Enter it with its sign if present. Blank, "DS," or "SPH" means no astigmatism — leave it empty. CYL and AXIS go together. |
| AXIS | Orientation of the astigmatism correction, a whole number 1-180 | Enter only when CYL is present. It is degrees of rotation, not a power — never round it. |
| ADD | Added reading power, used for bifocals and progressives | Enter only for progressive, bifocal, or reading lenses. Often one value for both eyes (e.g. +2.00). |
| PRISM / BASE | Corrects eye-alignment issues; shown with a base direction | Most people have none. Many budget retailers cannot make prism lenses — check first. |
| PD (Pupillary Distance) | Distance between your pupils, in millimeters | Required to center the lenses. Often missing — see the PD section below. |
A few field-level rules that trip first-timers up:
- Signs matter enormously. A +3.00 and a -3.00 are opposite lenses, so copy the plus or minus exactly.
- CYL and AXIS travel together. If one is filled in, the other must be. A CYL value with no AXIS is incomplete — go back to your prescription, not your best guess.
- Single-vision vs progressive is your choice at checkout, but you can only order progressives if your prescription includes an ADD value.
PD: the number that is usually missing
Pupillary distance (PD) is the millimeter measurement between the centers of your pupils, and it sets where the optical center of each lens sits. Get it wrong and even a perfectly powered lens can cause eye strain. It is frequently left off your written prescription, because it is a fitting measurement rather than a refraction value. You have a few options:
- Ask your eye doctor or the front desk to add it — many will. A single PD is one number (e.g. 63 mm); a "dual PD" is two, one per eye (e.g. 31.5 / 31.5), used mainly for progressives.
- Measure it at home with a ruler and a mirror, or a phone app. This is doable but error-prone, so measure two or three times.
- Use a retailer's built-in PD tool. Several online sellers offer a digital PD measurement, removing the guesswork — the easiest path for first-timers.
A typical adult PD falls roughly in the 54-74 mm range, and children's are smaller. If your number lands far outside that, re-measure before ordering.
A worked example
Suppose your prescription reads:
- OD: -2.00 -0.75 x 180, ADD +2.00
- OS: -1.75 DS, ADD +2.00
- PD: 62
Translated for an online form: the right eye gets Sphere -2.00, Cylinder -0.75, Axis 180 (mild nearsightedness plus a little astigmatism). The left eye gets Sphere -1.75 only — "DS" means no astigmatism, so leave Cylinder and Axis blank. The ADD +2.00 means you would pick progressive or bifocal lenses for reading correction, or single-vision (ignoring the ADD) for distance-only glasses. PD 62 goes in the pupillary-distance field. Enter those values exactly, pick your lens type, and you have ordered correctly.
Where to enter it: retailer picks by need
Once you can read your prescription, the question is which online retailer makes entering it easiest and gets your lenses right. Based on each retailer's published lens range, order flow, and return policies, here is how three popular options compare.
| Retailer | PD help at checkout | Best lens range for | Return / remake window (per published policy) | Best for |
|---|---|---|---|---|
| EyeBuyDirect | Digital/app-based PD measurement | Budget single-vision, blue-light, basic progressives | 14-day return policy | First-timers and backup pairs on a tight budget |
| Yesglasses | Digital PD measurement | High-index for strong scripts, progressives | 30-day return window | Stronger prescriptions and progressive wearers |
| Glasses.com | Virtual try-on; PD via app/support | Designer frames, name-brand lenses, insurance | 30-day / brand-backed returns | Designer frames and using vision benefits |
Check current options: EyeBuyDirect · Yesglasses · Glasses.com
A bit more on each, mapped to the prescription you just decoded:
- Straightforward numbers, tight budget: EyeBuyDirect is the easy on-ramp, with a field-by-field order form and a digital PD tool. The trade-off is a shorter 14-day return window, so confirm your numbers before you buy.
- Strong script or first progressives: when SPH runs high (around -6.00 or beyond) or your prescription includes an ADD, lens thickness and accuracy matter more than price. Yesglasses is worth comparing for its high-index lens options and a typically longer 30-day return window.
- Designer frames or vision benefits: Glasses.com leans into virtual try-on and name-brand selection. You still enter the same SPH/CYL/AXIS/ADD/PD values; the difference is frame brands and benefit handling, not the prescription form.
PD-tool availability and return windows change, so check each retailer's current help page before ordering. The prescription-entry mechanics are identical everywhere — copy each field exactly, match OD to right and OS to left, and add PD.
A quick pre-checkout checklist
Before you hit "add to cart," confirm:
- Prescription is current and is the eyeglass version, not contacts.
- SPH for each eye is copied with the correct + or - sign, and right-eye values sit in the OD/Right fields.
- CYL and AXIS are both present or both blank for each eye.
- ADD is entered only if you are buying progressives, bifocals, or readers.
- PD is filled in — from your doctor, a careful home measurement, or the retailer's tool.
If anything is unclear, or your prescription includes prism or values you cannot interpret, that is a question for your eye doctor — not something to guess at checkout.
Frequently Asked Questions
Can I buy glasses online without my PD?
You can, but you should not skip it. PD centers the lenses, and a wrong (or guessed) PD can cause eye strain. Ask your eye doctor to add it to your prescription, measure it carefully at home, or use a retailer that offers a digital PD tool — several online sellers do, which is the lowest-risk option for first-timers. Check the retailer's current help page to confirm the tool is available.
What does "DS" or "SPH" mean in the cylinder column?
"DS" (diopters sphere) and "SPH" both mean there is no astigmatism correction for that eye. Leave the CYL and AXIS fields blank for that row. If only one eye shows DS, the other eye may still have a cylinder value — enter each row independently.
My prescription is expired. Can I still order online?
No — and a reputable retailer will ask you to confirm an unexpired prescription. An expired script means it is time for a new eye exam, which is a medical step, not an online workaround. Book the exam, get the updated numbers, then shop.
Is the eyeglass prescription the same as my contact-lens prescription?
No. A contact-lens prescription is brand-specific and includes a base curve and diameter; an eyeglass prescription does not, and the powers can differ. Use only your eyeglass prescription for glasses, and ask your eye doctor for it specifically if you only have the contacts version.
What if my prescription includes "prism"?
Prism corrects eye-alignment issues and is shown with an amount and a base direction. Not every online retailer can produce prism lenses, and some budget tiers exclude them. If your prescription lists prism, check the retailer's lens options before ordering and confirm with your eye doctor that the values are current.
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