There’s no shortage of eye-care professionals who are skeptical about buying frames and lenses online. “These are custom-made devices. It’s not like buying a box of Cheerios,” explains Dr. Andrea Thau, an optometrist and president of the American Optometric Association. Prescription glasses, according to this camp, are complex medical devices—especially for people who need progressives or other multi-focal lenses, which require complicated measurements best taken while patients are wearing the frames they’ve selected. And once a pair of glasses is delivered, they say, the lenses should be checked to make sure the prescription is correct and the frames adjusted for fit.

But Stefanie Rodrigues, director of operations for Eyeglasses.com, thinks the main objection about buying glasses online isn’t really about the quality of glasses sold by online vendors but about the competition these vendors present to traditional eyeglass retailers. Most lenses, including progressives, are “not a big technical challenge for our lab,” she claims. When there is a problem, her company will remake the lenses at no extra charge. And, she adds, that doesn’t happen very often. “People think if they pay more, that means better vision. It doesn’t,” Rodrigues says.

But to make sure you’re really looking out for yourself when buying glasses online, follow these tips.

Research the website. Some online retailers, such as Warby Parker, Zenni Optical, and EyeBuyDirect, have top marks from the Better Business Bureau. Others don’t do so well, including EZContacts.com and GlassesUSA.com. Look for a report online at the Better Business Bureau (bbb.org). Also, see what others are saying by using a web search with the name of the company and terms like “reviews” and “complaints” before buying glasses online.

Resist buying frames you can’t try on. Many websites offer tools that let you test frames virtually by uploading a photo of your face. But trying on frames in the real, nonvirtual world is the only way to tell whether they’re comfortable and may give you a clue that they’re poorly made, says Adam Gordon, clinical professor of optometry at the University of Alabama at Birmingham. Before buying glasses online, you can find frames locally or use a website that will let you try them on at home, like Glasses.com, which sells designer frames and will send you one pair of glasses to try for 15 days, complete with prescription lenses (single vision only).

Examine the return policy and warranty. A retailer’s policies are especially important when buying online, where typically you must pay for your glasses before you receive them. Find out if the online seller will remake your lenses if there’s a problem or error.

Enter your prescription carefully. All those numbers and unfamiliar terminology, such as “axis,” “sphere,” and “cylinder,” can make prescriptions complicated. It’s easy to blunder when transferring the data to a website form. Some retailers may ask you to upload an image of the prescription to avoid potential errors.

Check your vision. If you have difficulty seeing with your new glasses, ask the online retailer to verify that the lenses were created using the proper prescription. If that checks out, go back to your doctor, who can recheck the lenses and make sure a mistake wasn’t made during your examination.

Know when you need a pro. If the frames need adjustment, many websites provide instructions on doing the job yourself. But Gordon says it’s less risky to have a professional do it. Many walk-in retailers will adjust glasses purchased elsewhere, like if you bought your glasses online, though you may have to pay for this service.

Editor's Note: This article also appeared in the February 2017 issue of Consumer Reports magazine.