Don't buy blue-light glasses to “protect your eyesight,” and don't believe that “a few months facing a screen ruins your eyes,” but treat swollen, painful, red eyes as an emergency

Cost

Free, and you save the several hundred to over 1000 CNY markup on the lenses.

What you get

A 2023 Cochrane systematic review included 17 randomized controlled trials, each with 5 to 156 people, followed from less than 1 day to 5 weeks. Because there was too little data, the trials recruited very different people and the follow-up times were inconsistent, the authors did not pool them into one total. All the results below are compared with lenses without blue-light filtering. With follow-up under a week, self-reported eye fatigue “may make no difference,” with low certainty of evidence. In one trial of 120 people, the two groups differed by 9.76 units. The plausible range for that difference is 95% CI −33.95 to 53.47. The range spans both sides of zero, which means no difference can be seen. Critical flicker fusion frequency is an objective measure of eye fatigue, and the two groups “may make little to no difference,” with low certainty. The best vision achievable with corrective glasses “probably has no effect.” The two groups differed by 0.00 logMAR (95% CI −0.02 to 0.02). This came from only 1 study of 156 people, with moderate certainty. The effect on daytime alertness is unclear (2 trials, 42 people, very low certainty). The review also found no evidence supporting protection of the macula at the back of the eye

Notes

What screens bring is eye strain and dry eye, which show up as sore, dry eyes and blurry vision after looking for a long time. Resting and blinking more eases it. It recovers, which is not the same as “damaging your eyes.” This statement is the consensus of ophthalmology and not a conclusion of the Cochrane review in the sources column, so it gets only a grade of C. What can cause irreversible eye damage within a short time is a strong light source such as welding arc light, ultraviolet light or a laser. Eye injury from welding arc light is called photokeratitis (电光性眼炎) and is a legally recognized occupational disease. What blocks it is goggles and a face shield, not blue-light lenses; see §19.10 (protection against dust, noise and chemical poisons). What you should guard against when staring at a screen through an all-nighter is not the screen itself but one exception: if your eyes are swollen, painful and red, you see rainbow rings around lights, and you also have headache, nausea and vomiting, that is an attack of acute angle-closure glaucoma, which can crush the optic nerve within a few days. Go to an eye emergency room that same day; see §13.6 (eye emergencies). Pupils that widen in the dark and a long time looking down, which pushes the lens forward, are the two triggers, and those at high risk are people over 50, people who are farsighted, and people with a shallow front chamber of the eye. Dry eye from screens, if it drags on, can also become a chronic condition that needs a doctor, and it will not go away with a night's sleep. If your eyes are always uncomfortable, or your vision is truly falling, go to an eye doctor to find out why; don't think swapping lenses on your own settles it. For preventing nearsightedness in children and teenagers, see §30.4, §30.12, §30.9 (2 hours outdoors every day, cycloplegic eye exams, don't buy products that claim to “cure nearsightedness”).

Evidence grade

A : Specific numbers from meta-analyses, large cohorts or randomized trials; for law and policy, the statute or official text.

Sources

1. Singh S, Downie LE, Anderson AJ, Keller PR, White SJ, Ang M, Wolffsohn JS (2023). Blue-light filtering spectacle lenses for visual performance, sleep, and macular health in adults. Cochrane Database of Systematic Reviews, 8, CD013244. https://doi.org/10.1002/14651858.CD013244.pub2

Translated from the Chinese original. Original book, section 6, tip 16. Content may be out of date and rules differ by place. When you actually deal with an agency, a doctor or a court, follow what local officials, doctors and lawyers tell you. Disclaimer