Short-sightedness

Does screen time cause short-sightedness? What the studies show

Screens and short-sightedness rise together, but that does not prove one causes the other. What the large reviews found, what they cannot tell us, and the changes worth making on Monday.

by Dr Chan Li Yen · MBBS, MOphth (UM), Fellowship in Paediatric Ophthalmology & Strabismus

Dr Chan Li Yen, consultant paediatric ophthalmologist, MMC 43128, NSR 132980 · Eagle Eye Centre Kuala Lumpur, Petaling Jaya

11 min read · 1,959 words

Key takeaways

Studies link more screen time with more short-sightedness, but none has shown that screens cause it. The International Myopia Institute's 2021 review called the evidence weak and inconsistent.
A 2025 review of 45 studies (335,524 participants) found 21 percent higher odds of myopia for each extra daily hour of screen time. It is observational and describes groups, not one child. A 2020 review pooling five studies found no association.
Children who use screens more also tend to spend more time indoors and doing close work. Time outdoors is protective and more years of schooling raise risk, so these can distort the screen link.
No study shows that cutting screen time slows myopia that has already started. Treat distance, breaks and where devices live as comfort habits, not proven prevention.
For a child already short-sighted, regular measurement of how fast the eyes change matters more than a screen limit. A short-sighted parent raises a child's chance, so family eye checks make sense.

If your child's number went up this year, it is natural to look at the tablet on the sofa and wonder. The honest answer is that studies link more screen time with more short-sightedness (myopia, rabun jauh), but they have not shown that screens cause it.

That gap between "linked" and "causes" is the whole story, and it changes what is worth doing on Monday. Here is what the large reviews found, why they cannot settle it, and what a family can sensibly change.

Does screen time cause short-sightedness in children?

It has not been proven. Studies find that children who spend more hours on screens are more likely to be short-sighted, but screens are not shown to be the cause. The International Myopia Institute (IMI), in its 2021 review of risk factors, called the evidence linking screen time to myopia weak and inconsistent.

The same review points to two factors with firmer support. More years of schooling were confirmed as a cause by a type of genetic analysis (Mendelian randomisation). And more time outdoors was confirmed as protective in randomised trials. Screens sit in a murkier place, because they travel with other things: close reading, long school days and less time outside.

What do the big studies actually show?

The biggest recent review found a clear association, and the earlier ones found a weaker or mixed one. All of them are observational, meaning they count what children already do and compare their eyes. None of them assigned screens to some children and not others.

The largest, by Ha and colleagues in 2025, pooled 45 studies with 335,524 participants, average age about 9. For each extra hour of daily screen time, the odds of myopia were 21 percent higher (odds ratio 1.21). An odds ratio compares the odds of myopia in one group with another. In the curve the authors drew, one hour a day carried an odds ratio of 1.05 and four hours 1.97. They suggested a possible safe threshold under one hour, but that is an estimate from the data, not a tested limit. It included television as well as phones and tablets.

One caution on the number. A 21 percent rise in odds does not mean that 21 in 100 more children become short-sighted. It says how much more often myopia turned up in children with an extra hour of screen time, across studies that measured screen time in different ways. It describes groups of children, not what your child's eyes will do.

An earlier review, Foreman and colleagues in 2021, looked at smartphones and tablets in children and young people up to age 33. Smart device use alone gave an odds ratio of 1.26, with a confidence range that just reached 1.00, and 1.77 when computer use was added. The authors wrote that smart devices "might be" associated with myopia. Every study measured screen time by questionnaire, and about a quarter did not adjust for other factors.

A 2020 review by Lanca and Saw, with 15 studies and 49,789 children, called the results mixed. Seven studies found an association, and when five studies were pooled, the odds ratio was 1.02, which is no association.

Why can't these studies prove that screens cause it?

Because the children who use screens more also differ in other ways, and those differences can produce short-sightedness by themselves. The word for this is confounding: a third factor that is mixed up with the one you are studying.

Think of a child who is on a tablet three hours a day. That child is probably indoors more, and probably reads and studies close up too. Time outdoors has a real protective effect. In a 2017 meta-analysis, trials that added outdoor time cut the risk of becoming short-sighted to about half (risk ratio 0.54). So a link between screens and myopia could be partly a link between being indoors and myopia.

There are also measurement problems. Screen time was reported by questionnaires in every study in the Foreman review, and none used a reliable measure. Parents and children estimate poorly. And the studies mix kinds of screen: a child watching television from across the room is not doing the same thing as a child reading a phone held close.

The short version, and the version I would give a parent across the desk: screens may add to the risk, they may just be a marker for indoor, close-up days, and the current studies cannot tell which. Either way, the sensible response is similar.

What about the lockdown years, when children were on screens all day?

The lockdown data are a useful clue. They show a shift in the youngest children, but they cannot separate screens from lost outdoor time. A 2021 study of 123,535 children aged 6 to 13 in China compared school photo-screenings in 2020, after home confinement, with the five years before.

Children aged 6, 7 and 8 shifted by about 0.3 dioptres towards short-sightedness. At age 6, myopia was found in 21.5 percent against 5.7 percent in the highest earlier year. Children aged 9 to 13 barely changed. Home confinement meant much less time outdoors and much more screen time at once, so the study cannot say which one did it. The authors also note that the eyes were measured without drops, which can overstate myopia.

Two things are fair to take from it. Young eyes may respond more to changes in daily habits than older ones. And a long stretch indoors is worth avoiding for reasons that go beyond screens. How outdoor time works, and what it can and cannot promise, is in two hours outside.

What should we actually change at home on Monday?

Change the things that are cheap and harmless whatever the final answer turns out to be: distance, breaks, where the device lives, and time outdoors. None of these is proven to prevent myopia, and I would rather say that plainly than sell a rule.

Distance. The Hong Kong Student Health Service advises keeping at least 50 cm from a computer screen, 40 cm from a tablet or e-book and 30 cm from a smartphone. That is a government guide, not a trial result. Our article on screen size looks at why distance matters more than the size of the screen.
Breaks. The same service suggests resting 20 to 30 seconds after every 20 to 30 minutes of screen use. Treat it as a comfort habit. The article on the 20-20-20 rule sets out what is and is not known.
Where the device lives. A charging spot in a shared room, and a clear end to each session, makes a limit easier to keep without arguments. This is a household habit, not something a study has tested for eyes.
Outdoors. A daily outdoor block has the firmest evidence of anything on this list, for preventing short-sightedness in children who are not yet short-sighted.

The same Hong Kong guide suggests keeping recreational screen time to two hours a day or less for ages 6 to 12. Treat the figure as one health service's guide. It is not a threshold proven to protect eyes, and the Ha review suggests there is no sharp line, only odds that rise gradually.

What if my child is already short-sighted?

Then limiting screens alone is unlikely to be the main tool. The 2017 outdoor-time meta-analysis found that time outdoors did not slow progression in eyes that were already short-sighted, and no study has shown that cutting screens does either. Treat screen habits as general eye comfort, and put the weight on measuring how fast the eyes are changing.

That means regular checks, with the power measured the same way each time. If the number is rising fast, ask about options for slowing it down. They are described, with how sure the evidence is, in slowing myopia down and atropine drops for myopia.

Family history matters more than most parents realise. The American Academy of Ophthalmology says a short-sighted parent raises a child's chance of being short-sighted, and the NHS says it often runs in families. If one of you is short-sighted, an early check for the children is a sensible step, and it is a good moment to check your own eyes too. For the wider picture, see why short-sightedness is rising.

See an eye doctor sooner if…

The glasses seem weaker within a few months, or your child sits closer to the board or screen again.
Your child squints, rubs the eyes or gets headaches after only a short spell of close work.
Vision suddenly drops in one eye, or one eye becomes much worse than the other.
Your child sees flashes of light, a new shower of floaters or a curtain over part of the vision: same-day care.

Common questions

Does screen time cause myopia in kids?

It has not been proven. Studies link longer screen time with more myopia, but they are observational and cannot rule out other causes such as less time outdoors. The International Myopia Institute's 2021 review called the evidence linking screen time to myopia weak and inconsistent.

How many hours of screen time is too much for a child's eyes?

No safe limit has been proven. A 2025 review found each extra daily hour went with 21 percent higher odds of myopia and suggested a possible threshold under one hour, but that is an estimate from observational data. The Hong Kong Student Health Service advises no more than two hours of recreational screen time a day for ages 6 to 12, as a health guide, not a trial result.

Is a phone worse for myopia than a tablet or TV?

The studies cannot say. Reviews mix device types, and television is usually watched from further away. Distance matters: the Hong Kong guide suggests at least 30 cm for a phone, 40 cm for a tablet and 50 cm for a computer.

Did lockdown and online classes make children more short-sighted?

They may have, in the youngest children. A study of 123,535 Chinese children found a shift of about 0.3 dioptres at ages 6 to 8 after home confinement, and little change at 9 to 13. It cannot separate screen time from lost time outdoors, and the eyes were measured without drops.

Will cutting screen time slow my child's myopia?

There is no study showing that it does. The 2017 meta-analysis on outdoor time found that time outdoors helps prevent myopia starting but did not slow progression in eyes already short-sighted. Slowing options are discussed with an eye doctor after the eyes are measured.

Is close reading and homework a bigger risk than screens?

The studies cannot rank them. The International Myopia Institute's 2021 review says more years of schooling is confirmed as a cause by genetic analysis, while links between near work and myopia are generally weak and inconsistent. Screens, reading and homework often come together, so the data cannot pull them apart.

Does a short-sighted parent mean the child will be too?

It raises the chance but does not decide it. The American Academy of Ophthalmology says a short-sighted parent raises a child's chance of being short-sighted, and the NHS says it often runs in families. An early eye check for the children is a sensible step.

References

JAMA Network Open · Digital screen time and myopia: a systematic review and dose-response meta-analysis (2025) · pubmed.ncbi.nlm.nih.gov
The Lancet Digital Health · Association between digital smart device use and myopia: a systematic review and meta-analysis (2021) · pubmed.ncbi.nlm.nih.gov
Ophthalmic and Physiological Optics · The association between digital screen time and myopia: a systematic review (2020) · pubmed.ncbi.nlm.nih.gov
Investigative Ophthalmology & Visual Science · IMI Risk Factors for Myopia (2021) · pubmed.ncbi.nlm.nih.gov
Acta Ophthalmologica · Time spent in outdoor activities in relation to myopia prevention and control: a meta-analysis (2017) · pubmed.ncbi.nlm.nih.gov
JAMA Ophthalmology · Progression of myopia in school-aged children after COVID-19 home confinement (2021) · pubmed.ncbi.nlm.nih.gov
Hong Kong Student Health Service · Myopia (short-sightedness) guide · www.studenthealth.gov.hk
American Academy of Ophthalmology · Nearsightedness (myopia) · www.aao.org
NHS · Short-sightedness (myopia) · www.nhs.uk

By Dr Chan Li Yen. General information only. It does not replace a consultation. If you are worried about your child's eyes or vision, please see an eye doctor.