Is it ok to buy progressive lenses online

Buying glasses online has its advantages: You have a lot more frames to choose from than in your local optician's office, they often cost less, and you can even try some on from the comfort of your couch. But as we talk about in our guide to the best places to buy glasses online, buying online isn’t a good choice for everyone. If you have a strong or complicated prescription, for example, you may be better off buying glasses in person, with the help of a professional. Ditto if you have fitting issues. Even if you don’t have special prescription needs or fit problems, buying glasses online can still be risky.

According to The Vision Council, a nonprofit trade association, more than 150 million American adults wear prescription eyeglasses (PDF). If you’re nearsighted (a condition called myopia), this means you can see things clearly only if they’re close to you. In this case, your eye focuses an image at a point in front of your retina, causing it to be blurry. People with hyperopia, or farsightedness, have the opposite problem and can see only faraway things clearly. In this situation, the eye focuses an image behind your retina, also causing blurriness. In either case, putting a curved lens (either convex or concave) in front of your eye causes the light to refract, or bend, differently. This effectively moves where the image focuses, either forward or backward, so that it hits the retina correctly. If you’re nearsighted, you have a negative prescription. If you’re farsighted, those numbers are positive.

When an optician fits your eyeglass frames, first they check to see exactly where you’re looking through the lenses, and then they usually mark it on the lens of the frames you try on. This mark indicates where the center of vision should go, which ensures that you’re looking through the exact spot that corrects your focus.

One of the problems with buying glasses online is that you have no optician at your house to assess what part of the lens you’re looking through. Generally, when you order online, the company puts the vertical center of vision (as opposed to the horizontal center of vision, which is the PD, or pupillary distance) in the geometric center of the lens. One company we evaluated for our online-glasses guide, Felix + Iris, includes a marker in its at-home try-on boxes for you to mark the center of your vision on each test lens. When ordering glasses, you can indicate if you want the company to wait until it gets the try-on frames back so that it can consider your marks when producing your lenses. But other companies don’t provide a way for you to indicate your vertical center of vision. Depending on how your frames fit, the geometric center of the lens may not be the part you’re looking through.

For our online-glasses guide, I took glasses I’d ordered from all six companies we tested to Dr. Neil Pence, associate dean for clinical and patient care services at the Indiana University School of Optometry. He checked them on a lensometer and found that the prescriptions were correct in all my lenses. In all cases, however, the online glasses companies had put my center of vision in the geometric center of the lens. Check out where my pupils are in the self-portrait above: I’m looking through the upper third of the lens, significantly above where my vision is best corrected.

Another test panelist for our glasses guide, strategy editor Ganda Suthivarakom, also had this problem with the glasses she ordered from Jins and from Warby Parker (neither of which provides a way for you to indicate where your vertical center of vision is). In her case, the issue was exacerbated by her low nose bridge, which causes glasses to sit lower on her face, and a fairly strong prescription (about -7 on both sides). She took her glasses to an optician, who again found that the vision in both lenses was centered in the middle, well below her line of sight.

For many people, this misalignment won’t feel like a significant problem. It’s not a big deal for me since I have a pretty weak prescription (around +1 in both eyes). But the stronger your prescription, the more likely such misalignment will bother you. “As a general rule ... if your prescription is from about -4 or a +4, it’s going to be much more critical that your center of vision be aligned perfectly,” Dr. Neil Pence told me. For Ganda, it was a dealbreaker: “Everything below eye level looks distorted, making it very difficult to wear these glasses without feeling a little cross-eyed,” she said. “I also couldn't read things without pushing my head down.”

The diagram above illustrates this effect. At the top is a cross-section of a lower-strength prescription lens; at the bottom, a higher-strength one. The latter lens is generally thicker because it has to correct the image more, which requires that light bends at a higher degree, Pence explained. Because the lens is thicker at the edges with a higher prescription, it matters more if you’re looking through a part of the lens that is not quite at the center of vision. The line of sight on the thinner lens, in contrast, has a similar thickness to the center of vision, and therefore the difference is less noticeable.

This is called creating prism. The thicker the prism, the more it deflects the image, as opposed to passing straight through in the center. So if your glasses are misaligned, it won’t blur your vision totally; instead, things will just look “off,” Pence said.

According to several eye-care professionals I interviewed, whether peering through misaligned lenses will bother you is personal. “Some people are going to be more sensitive to it than others,” said Pence. “So we might have someone who has a prescription of -2, but they cannot tolerate it being misaligned.”

Nancy Kirsch of the SUNY College of Optometry agreed. “Some people who have tiny, little prescriptions are really critical, and some people who have -10 and -12 are very relaxed about what they're looking for,” she told me in a phone interview. The size and shape of the lenses in the frames may make misalignment problems worse, Kirsch said. As may the current trend toward larger frames, which can easily leave eyes misaligned by as much as 7 or 8 millimeters.

As for Ganda’s experience, if she had not gone to the optometrist to have her online glasses checked, she would not have known the cause of the problem: Was the prescription incorrect? Was the fit just off? The companies we recommend in our full guide have good return policies, and you should take advantage of them if your glasses aren’t a good fit for any reason.

Next time, Ganda is sticking with her local optometrist. “The advice I'd impart to a friend is: If you have a high prescription, or a new prescription, or a difficult-to-fit face, don't buy online.”

Mentioned above

• After testing comparable frames and lenses from seven online retailers, we recommend starting your search for prescription eyeglasses at Eyebuydirect.

  The Best Places to Buy Glasses Online 

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