To order glasses online, you need four things: a current eyeglass prescription, your pupillary distance measurement, your frame size preferences, and your lens selections (material, coatings, and type). Most people already have the prescription but are missing the pupillary distance, which is the one number that trips up first-time online buyers. Here’s everything you need to gather before you check out.
Your Eyeglass Prescription
Every online retailer will ask you to enter the values from your written prescription. Under the FTC’s Eyeglass Rule, your eye doctor is required to hand you a copy of your prescription immediately after your exam, whether you ask for it or not, and before trying to sell you glasses. If you weren’t given one, call the office and request it. They cannot legally refuse.
A standard prescription includes several fields, and each eye is listed separately. Your right eye is labeled OD and your left eye is labeled OS. Here’s what the numbers mean:
- Sphere (SPH): The main lens power that corrects your vision. A minus sign means you’re nearsighted; a plus sign means you’re farsighted.
- Cylinder (CYL): The amount of astigmatism correction you need, if any. Not everyone has a value here.
- Axis: A number between 1 and 180 that tells the lab which angle to orient your astigmatism correction. This only appears if you have a cylinder value.
- Add: Additional magnifying power for reading or close-up work, used in bifocal and progressive lenses. This is typically present only for people over 40 with presbyopia.
Double-check that your prescription hasn’t expired. Most states set expiration dates of one to two years, and the expiration date should be printed on the prescription itself. Online retailers won’t fill an expired prescription.
Your Pupillary Distance
Pupillary distance (PD) is the distance in millimeters between the centers of your two pupils. The lab uses this number to center the lenses so the optical “sweet spot” lines up with where your eyes actually look through the frame. If it’s off, you can experience eyestrain, blurriness, or headaches.
Some doctors include PD on your prescription, but many don’t because they consider it a fitting measurement rather than a prescription value. If yours isn’t listed, you can measure it at home with a millimeter ruler. If you don’t have one, search for “printable mm ruler for eyeglasses” and print it at 100% scaling.
Measuring PD by Yourself
Stand about 8 inches from a mirror. Hold the ruler against your brow. Close your right eye and align the ruler’s 0 mm mark with the center of your left pupil. Then, looking straight ahead, close your left eye and open your right. The millimeter mark that lines up with the center of your right pupil is your PD.
Measuring PD With a Friend
Face each other about 8 inches apart. Place the ruler on the bridge of your nose. Cover your left eye while your friend aligns the 0 mm mark over the center of your right pupil. Then cover your right eye and open the left, and have your friend read the mark over your left pupil. For the best accuracy, repeat this three times and average the results.
Most adults have a PD somewhere between 54 and 74 mm. Some online retailers ask for a single (binocular) PD, while others ask for dual PD, which is the distance from each pupil to the center of your nose, listed separately. If you measured binocular PD and the site wants dual, dividing by two gives a close approximation for most faces.
Frame Size and Fit
Ordering the wrong frame size is one of the most common mistakes when buying glasses online. Every pair of glasses has three measurements, usually printed on the inside of the temple arm, separated by dashes or small squares.
- Lens width: The first number. It measures the width of each lens in millimeters, not including the surrounding frame material.
- Bridge width: The second number. This is the shortest span between the two lenses, and it determines how the frame sits on your nose. A smaller bridge fits narrower noses; a larger one fits wider noses.
- Temple length: The third number. This measures the arm from the hinge screw to the tip that hooks behind your ear. Common lengths are 135, 140, 145, and 150 mm.
The easiest way to find your size is to check a pair of glasses you already own and like the fit of. Look at the inside of the temple arm for three numbers. If you can’t find them, most online retailers publish the measurements for every frame they sell, and some offer virtual try-on tools that use your phone’s camera to approximate fit.
Choosing Your Lens Type
After entering your prescription and frame, you’ll be asked to pick a lens type. If your prescription only has sphere (and possibly cylinder) values, you need single-vision lenses. If your prescription includes an “Add” power, you’ll choose between bifocal and progressive lenses.
Progressive lenses deserve extra attention when ordering online. They require a measurement called segment height, which is the vertical distance from the bottom edge of the lens to the center of your pupil while you’re wearing the frame. This tells the lab exactly where to position the reading zone. If segment height is off, you’ll find yourself tilting your head awkwardly to read or struggling to find a clear zone. Some online retailers calculate this automatically from the frame dimensions, while others ask you to measure it yourself using a marked-up photo method. If you’re ordering progressives online for the first time, look for a retailer that walks you through this step or handles it for you.
Lens Material and Index
Lens index refers to how efficiently the lens material bends light. Higher-index lenses are thinner and lighter, which matters more as your prescription gets stronger. Here’s a general guide:
- 1.50 index: Standard plastic. Best optical clarity and lowest cost. Works well for mild prescriptions.
- 1.56 to 1.61 index: Slightly thinner with good transparency and durability. A solid choice for low to moderate prescriptions.
- 1.67 index: Noticeably thinner than standard lenses. A practical pick for moderate to strong prescriptions, and usually the best value at higher powers.
- 1.74 index: The thinnest option available. Recommended for very strong prescriptions where lens thickness would otherwise be cosmetically bulky.
If your prescription is mild (under roughly +/- 2.00), paying extra for high-index lenses won’t make a meaningful difference in thickness. Save the upgrade for prescriptions where the edges would otherwise look noticeably thick.
Lens Coatings Worth Considering
Most online retailers offer several add-on coatings. Not all of them are equally useful.
Anti-reflective coating reduces glare and reflections on the lens surface, which makes a visible difference when driving at night or appearing on video calls. It’s one of the most universally recommended upgrades. Anti-scratch coating adds a harder surface layer, and many retailers include it by default. Photochromic lenses darken automatically in sunlight, functioning as both regular glasses and sunglasses, which is convenient if you don’t want to carry two pairs.
Blue-light-blocking lenses are heavily marketed for reducing digital eye strain, but the evidence doesn’t support the claims. A study published in Investigative Ophthalmology & Visual Science tested blue-blocking lenses with and without anti-reflective coating and found no statistically significant improvement in any eye strain symptom, including blurred vision, dry eyes, headaches, tired eyes, or discomfort. Reading speed and eye movements were also unchanged. If you’re experiencing screen-related eye fatigue, taking breaks is more effective than buying a special coating.
Payment: FSA and HSA Cards Work
Prescription eyeglasses qualify as a medical expense under IRS rules, which means you can pay with your Flexible Spending Account (FSA) or Health Savings Account (HSA) card. This applies to online purchases just as it does in a physical store. The payment date recorded by your financial institution is the date that counts for your tax year, so keep that in mind if you’re spending down an FSA balance near the end of the year. Some vision insurance plans also reimburse online purchases, though you may need to pay upfront and submit a claim afterward rather than using the insurance directly at checkout.