Do blue light-blocking glasses reduce eyestrain? Review suggests no

Glasses that block blue light may not actually reduce eyestrain from looking at computer screens.

That's according to a new review, published Thursday (Aug. 17) to the Cochrane Database of Systematic Reviews, that assessed 17 randomized controlled trials of blue light-blocking glasses that included nearly 620 people in six countries. Based on these trials' results, glasses that "block" or "filter" the blue light emitted by computer screens don't appear to prevent or relieve eyestrain any better than glasses that don't filter blue light. 

Manufacturers sometimes also claim that, by blocking out some of the shorter, or blue, wavelengths of visible light, these glasses can help keep people's vision crisp and even improve their sleep. But the review found that the glasses have "probably little or no effect" on vision quality, and they have an "indeterminate" effect on sleep quality, with some studies reporting significant improvements and others reporting none.

Are these results surprising? Not really, according to experts.

Related: How do our eyes move in perfect synchrony?

The review showed "expected findings," Dr. Kevin M. Miller, a professor of clinical ophthalmology and chair of ophthalmology at the University of California, Los Angeles who was not involved in the study, told The Washington Post. "When the optical shop tries to talk you into the blue blocker, just say, 'I don't think so.'"

That being said, "there's no reason to think that blue-light filtering is harmful, other than the cost associated with adding it to your glasses," Dr. Craig See, an ophthalmologist and cornea specialist at Cole Eye Institute at the Cleveland Clinic in Ohio, told CNN. "The takeaway here is that it may not be doing as much as we were hoping."

The idea behind blue-light glasses partly comes from studies conducted in lab dishes and in animals that suggested blue light can damage the eyeballs, according to the American Academy of Ophthalmology (AAO). However, these studies didn't mimic the blue light exposure humans experience when staring at a computer screen, and so far, there's no clear link between such exposure and retinal damage or eye diseases. 

Symptoms of eyestrain, such as tired, burning or sore eyes and blurred vision, arise when people use computers because, as they're focused on the screen, they blink less than normal and their eyes dry out, The Washington Post reported. In addition, focusing on objects close to your face leads muscles in the eyes to contract, bending the eye's lens so as to focus light on the retina; over short periods, this can strain the eyes, and over long periods, it can contribute to myopia, or nearsightedness.

There is some evidence that blue light exposure in the evening can throw off our sleep-wake cycle, which normally involves the hormone melatonin increasing before bedtime. But you don't need special glasses to fix this problem — the AAO advises simply setting devices to dark mode in the evening and avoiding screens altogether in the one to two hours before bed.

The new review backs the AAO's stance that blue-light glasses may not be worth the purchase. 

"Our review doesn't support using a blue-light filtering lens if you're a healthy adult for the purpose of reducing eyestrain with computer use," Laura Downie, the review's senior author and an associate professor of optometry and vision sciences at the University of Melbourne in Australia, told the Post.

That said, the studies included in the new review have their flaws. They each included a small number of participants — only five to 156 — and ran for short periods of time, from less than a day to about five weeks. This limited the reviewers' ability to see whether the glasses might show noticeable benefits in the long-term, Downie told CNN.