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Reference topic 24: The Indoor Eye

Myopia in children: causes, screen time and time outdoors

ProbableEvidence grade: Probable. Good observational evidence with a plausible mechanism, or small or few trials.57 sources5 graded recommendationsTopic hub: Sleep and light

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In the late 1960s a team led by Francis A. Young tested the eyes of the Inuit residents of Barrow, Alaska. They put in drops, waited for the focusing muscles to let go, and measured how each eye bent light.1 A Bureau of Indian Affairs school had opened in the town in 1932, so everyone in the room had been sorted, by birth date alone, into one of two childhoods.

The 131 residents past the age of 41 had grown up in scattered coastal settlements, hunting and fishing, with little or no schooling. Two of them were nearsighted. Two out of 131.12

Mismatch card

The system

Emmetropization, the visual feedback loop that grows the eyeball to match its optics.

What it expects

A childhood of bright outdoor light, thousands of lux for hours a day, with things to look at near and far.

What it gets

Years of classrooms at a few hundred lux, and 87% of time spent inside a building.57

What happens in the gap

The eye overgrows, distance blurs for good, and a stretched retina carries lifelong risk.

The handrail

Two hours of daylight a day from school entry, early eye exams, and myopia control if progression starts (●●○)

Strength of evidence

●●○ Cluster-randomized trials and Mendelian randomization establish both causes, but effects are modest and the light mechanism is proven only in animals.

What this topic covers

  • ·An Eye That Builds Itself to Fit
  • ·The First Epidemic Had Desks
  • ·The Size of It Now
  • ·Years of School, Hours of Daylight

The practical version is in the book: Chapter 7, Light and Dark.

The handrail

Topic 41 holds the full daylight program. None of what follows replaces an eye care professional.

Each recommendation carries the strength of the evidence behind it. How the grades work.

  1. Get children outdoors about two hours a day, with a floor of one

    StrongEvidence grade: Strong. Multiple randomized controlled trials, or consistent large cohort studies with a well-understood mechanism.

    Evidence grade: Strong. Multiple randomized controlled trials, or consistent large cohort studies with a well-understood mechanism. for delaying onset·Evidence grade: Emerging. Early, small, animal-only, or actively contested. for slowing it once begun

    Two hours was Taiwan's school target and is widely endorsed.3913 China's plan specifies one to two,47 and the US National Academies at least one.4 Shade and cloud count: benefit appeared from 1,000 lux.36 It matters most from school entry on.26 Hats and sun sense apply (Topic 19).

  2. Break up close work, and treat screen time mainly as indoor time

    EmergingEvidence grade: Emerging. Early, small, animal-only, or actively contested.

    Cohn's 15 minutes outdoors per hour of near work has never been tested on its own.16 The screen association cannot be separated from the room.46

  3. Get eyes checked

    StrongEvidence grade: Strong. Multiple randomized controlled trials, or consistent large cohort studies with a well-understood mechanism.

    Vision screening at least once between ages 3 and 5,48 an eye examination before first grade,4 and sooner if a child squints at distance.

  4. If a child is already myopic and getting worse, ask about myopia control

    StrongEvidence grade: Strong. Multiple randomized controlled trials, or consistent large cohort studies with a well-understood mechanism.

    Evidence grade: Strong. Multiple randomized controlled trials, or consistent large cohort studies with a well-understood mechanism. for optical treatments·Evidence grade: Probable. Good observational evidence with a plausible mechanism, or small or few trials. for low-dose atropine

    The US Food and Drug Administration authorized the first myopia-control spectacle lenses in September 2025, for children 6 to 12, citing 71% less progression over two years.49 A similar design halved progression in a Hong Kong trial and another cut it substantially in Wenzhou,50 and dual-focus contact lenses cut it by 59%.51 Atropine eye drops work at higher doses and inconsistently at 0.01%,52 and a Cochrane review rates most estimates low certainty.53 Cautions: atropine brings light sensitivity and blurred near vision.54 Orthokeratology (lenses worn overnight to reshape the cornea) carries a small risk of corneal infection.51 Red-light devices can exceed laser safety limits and belong in supervised trials only.55

  5. Adults with high myopia, know the warning signs

    StrongEvidence grade: Strong. Multiple randomized controlled trials, or consistent large cohort studies with a well-understood mechanism.

    A burst of new floaters, flashes of light, or a dark curtain across your vision means a same-day visit to an eye doctor or emergency room.56

The skeptic's corner

The case against this topic, from the research itself.

The main objection is genetic: myopia runs in families, and twin studies put its heritability at 84 to 90%.41 True, and largely beside the point: heritability describes the spread within one population under one set of conditions, not why a whole population changed. "Gene pools simply do not change that fast," as the myopia researcher Ian Morgan puts it. He adds that most children who became myopic in the epidemic did not have myopic parents. Geneticists on the other side hold that heritability of 60 to 90% still makes genes the primary driver.42 A fair reading: genes set who is susceptible, and environment how many.

The light story rests mostly on animals, and no one knows how much light a child's eye needs.13 The effects in children are modest: Guangzhou's gap was nine percentage points over three years, and the eyes grew almost as long in both groups.35 Taiwan's national result came from an eye chart, not a measurement of focus, and careful measurements in Taipei show second-grade myopia still creeping up.3943 Even leading proponents of outdoor time call its effect on myopia already under way "more controversial."44

Screens deserve less blame than they get, and more than none. An early review found no overall association;45 a later, larger one found the odds of myopia rising about a fifth with each daily hour of screen time.46 All of it is observational, and none of it separates the screen from the room it is held in.

Terms this topic defines

Related topics

Sources cited above

  1. 1.Young, F.A., Leary, G.A., Baldwin, W.R., West, D.C., et al. (1969). "The transmission of refractive errors within eskimo families." American Journal of Optometry and Archives of American Academy of Optometry, 46(9), 676-685. https://doi.org/10.1097/00006324-196909000-00005 (the 1969 paper has no abstract online; the figures of 508 examined, 2 of 131 over age 41, and 51.4% of 284 aged 11-40 at a threshold of -0.25 D, together with the 1932 Bureau of Indian Affairs school and the use of a cycloplegic, are taken from the author manuscript and lecture material of Cordain et al. 2002)
  2. 2.Cordain, L., Eaton, S.B., Brand Miller, J., Lindeberg, S., et al. (2002). "An evolutionary analysis of the aetiology and pathogenesis of juvenile-onset myopia." Acta Ophthalmologica Scandinavica, 80(2), 125-135. https://doi.org/10.1034/j.1600-0420.2002.800203.x (the same review summarizes early surveys finding myopia in 0.4% of 3,624 eyes in Gabon and 1.2% of 1,123 eyes among East Greenland Inuit; its own hypothesis, that dietary hyperinsulinemia drives myopia, has no trial support and is not used here). Barrow was renamed Utqiagvik by a vote of 381 to 375 in October 2016: Anchorage Daily News (2016, October 13). "Barrow voters support name change to Utqiagvik." https://www.adn.com/alaska-news/rural-alaska/2016/10/13/barrow-voters-support-name-change-to-utqiagvik/
  3. 41.Hammond, C.J., Snieder, H., Gilbert, C.E., and Spector, T.D. (2001). "Genes and environment in refractive error: the twin eye study." Investigative Ophthalmology & Visual Science, 42(6), 1232-1236. https://pubmed.ncbi.nlm.nih.gov/11328732/ (226 identical and 280 fraternal twin pairs aged 49-79)
  4. 42.Verhoeven, V.J.M., Morgan, I.G., and Guggenheim, J.A. (2025). "Myopia is predominantly genetic or predominantly environmental?" Ophthalmic & Physiological Optics, 45(4), 911-917. https://doi.org/10.1111/opo.13464 (Morgan also notes that twin heritability rests on the assumption that identical and fraternal twins share environments equally, when identical twins are also more alike in education). Genes and schooling interact: Fan, Q., Verhoeven, V.J., Wojciechowski, R., Barathi, V.A., et al. (2016). "Meta-analysis of gene-environment-wide association scans accounting for education level identifies additional loci for refractive error." Nature Communications, 7, 11008. https://doi.org/10.1038/ncomms11008 (Morgan adds that measured variants account for perhaps 20% of the heritability; the genetic side holds that heritability of 60 to 90% still makes genes the primary driver)
  5. 13.Ashby, R., Harb, E.N., Ostrin, L.A., Flitcroft, D.I., et al. (2025). "IMI: The role of light in refractive development and myopia: Evidence from animal and human studies." Investigative Ophthalmology & Visual Science, 66(15), 5. https://doi.org/10.1167/iovs.66.15.5 (the review also notes that clinical recommendations for two hours outdoors are well supported epidemiologically while no evidence-based guideline yet covers specific light characteristics, and that no clinical recommendation can be made for light-based therapies; several authors disclose industry ties)
  6. 35.He, M., Xiang, F., Zeng, Y., Mai, J., et al. (2015). "Effect of time spent outdoors at school on the development of myopia among children in China: A randomized clinical trial." JAMA, 314(11), 1142-1148. https://doi.org/10.1001/jama.2015.10803 (1,903 first graders, mean age 6.6, October 2010 to October 2013; difference -9.1 percentage points, 95% CI -14.1 to -4.1, a relative reduction of about 23%; axial elongation 0.95 versus 0.98 mm, P=0.07)
  7. 39.Wu, P.C., Chen, C.T., Chang, L.C., Niu, Y.Z., et al. (2020). "Increased time outdoors is followed by reversal of the long-term trend to reduced visual acuity in Taiwan primary school students." Ophthalmology, 127(11), 1462-1469. https://doi.org/10.1016/j.ophtha.2020.01.054 (Taiwan screens uncorrected visual acuity in 1.2 to 1.9 million primary schoolchildren twice a year; the outcome is acuity of 20/25 or worse, a proxy for myopia rather than measured refraction; the trend moved from +1.58% a year before the policy to -2.34% after) (the Tian-Tian 120 program, from September 2010, urged 120 minutes outdoors a day; reduced uncorrected vision rose from 34.8% in 2001 to 50.0% in 2011, then fell every year to 46.1% in 2015)
  8. 43.Yang, Y.C., Fang, S.Y., Yang, H.Y., Wang, C.Y., et al. (2026). "Evolving patterns of childhood myopia in Taiwan: Effects of urbanization, digitalization, and outdoor activity policies." Taiwan Journal of Ophthalmology, 16(2), 294-302. https://doi.org/10.4103/tjo.TJO-D-25-00213 (cycloplegic refraction in grade 2 pupils; rural Yilan 24.00% in 2023; the share of children outdoors at least an hour on weekdays rose from 15.81% to 33.13%) (cycloplegic second-grade myopia 36.36% in 2013 and 39.39% in 2023)
  9. 44.French, A., Ashby, R., Karouta, C., Rose, K., et al. (2026). "Time outdoors and the prevention of myopia: School-based implementation works." Taiwan Journal of Ophthalmology, 16(2), 181-193. https://doi.org/10.4103/tjo.TJO-D-25-00206
  10. 45.Lanca, C., and Saw, S.M. (2020). "The association between digital screen time and myopia: A systematic review." Ophthalmic & Physiological Optics, 40(2), 216-229. https://doi.org/10.1111/opo.12657 (15 studies, 49,789 children; pooled odds ratio 1.02, 95% CI 0.96-1.08)
  11. 46.Ha, A., Lee, Y.J., Lee, M., Shim, S.R., et al. (2025). "Digital screen time and myopia: A systematic review and dose-response meta-analysis." JAMA Network Open, 8(2), e2460026. https://doi.org/10.1001/jamanetworkopen.2024.60026 (45 studies; odds ratio 1.21 per daily hour, 95% CI 1.13-1.30; the authors propose a possible threshold below one hour a day) (335,524 people)
  12. 47.Jan, C., Li, L., Keay, L., Stafford, R.S., et al. (2020). "Prevention of myopia, China." Bulletin of the World Health Organization, 98(6), 435-437. https://doi.org/10.2471/BLT.19.240903 (the 2018 State Council plan specifies one to two hours outdoors daily, no written homework in the first two school years, and limits thereafter; the authors call it a work in progress that mixes well-founded measures with popular beliefs)
  13. 4.National Academies of Sciences, Engineering, and Medicine (2024). Myopia: Causes, Prevention, and Treatment of an Increasingly Common Disease. The National Academies Press. https://doi.org/10.17226/27734 (Summary, Conclusions 5-1, 5-2 and 6-2; Recommendations 5-1 and 8-1; Chapter 5 on the Inuit studies) (the report blames the near work of newly compulsory schooling)
  14. 36.Wu, P.C., Chen, C.T., Lin, K.K., Sun, C.C., et al. (2018). "Myopia prevention and outdoor light intensity in a school-based cluster randomized trial." Ophthalmology, 125(8), 1239-1250. https://doi.org/10.1016/j.ophtha.2017.12.011 (693 first graders across 16 schools; one-year myopic shift 0.35 versus 0.47 D; 8 of 24 randomized schools withdrew). An earlier two-school study of the same idea: Wu, P.C., Tsai, C.L., Wu, H.L., Yang, Y.H., et al. (2013). "Outdoor activity during class recess reduces myopia onset and progression in school children." Ophthalmology, 120(5), 1080-1085. https://doi.org/10.1016/j.ophtha.2012.11.009
  15. 26.Chua, S.Y., Sabanayagam, C., Cheung, Y.B., Chia, A., et al. (2016). "Age of onset of myopia predicts risk of high myopia in later childhood in myopic Singapore children." Ophthalmic & Physiological Optics, 36(4), 388-394. https://doi.org/10.1111/opo.12305 (odds ratio 2.86 per year younger at onset for high myopia by age 11) (928 children)
  16. 16.Pärssinen, O. (2025). "Factors associated with the high prevalence of myopia and its decrease: A historical review." Acta Ophthalmologica, 103(8), 879-890. https://doi.org/10.1111/aos.70001 (reviewing Cohn's Lehrbuch der Hygiene des Auges, 1892, the Strasbourg Manifesto of September 1882, Widmark's Swedish comparison of 1882-1884 with 1904-1905, and Tscherning's finding of myopia in 32% of Copenhagen students versus 2% of peasants. Cohn's memory of candlelit writing lessons is Pärssinen's paraphrase. The review's own conclusion favors reducing near work over increasing outdoor time) (Widmark was Sweden's first professor of ophthalmology. Cohn examined 10,060 schoolchildren from 1865, counting only myopia of a diopter or more in both eyes: 1.4%, 2.0% and 3.0% in the three highest grades of five village schools; 44.0% in the top grade of Breslau's grammar schools; 55.8% in the upper grades of secondary schools; 78 to 81% among theology students at Tübingen. Widmark's average fell from 22.2% in 1882-1884 to 9.8% in 1904-1905, and in the two highest grades from 45.3% to 17.4%)
  17. 48.US Preventive Services Task Force; Grossman, D.C., Curry, S.J., Owens, D.K., et al. (2017). "Vision screening in children aged 6 months to 5 years: US Preventive Services Task Force recommendation statement." JAMA, 318(9), 836-844. https://doi.org/10.1001/jama.2017.11260 (a B recommendation targeting amblyopia rather than myopia; evidence judged insufficient below age 3)
  18. 49.US Food and Drug Administration (2025). FDA authorizes marketing of first eyeglass lenses to slow progression of pediatric myopia. https://www.fda.gov/news-events/press-announcements/fda-authorizes-marketing-first-eyeglass-lenses-slow-progression-pediatric-myopia (authorized September 25, 2025, via the De Novo pathway for children aged 6 to 12 at initiation; some wearers reported blur and halos)
  19. 50.Lam, C.S.Y., Tang, W.C., Tse, D.Y., Lee, R.P.K., et al. (2020). "Defocus Incorporated Multiple Segments (DIMS) spectacle lenses slow myopia progression: a 2-year randomised clinical trial." British Journal of Ophthalmology, 104(3), 363-368. https://doi.org/10.1136/bjophthalmol-2018-313739 (183 children aged 8-13; 52% less progression, 62% less axial growth); Bao, J., Huang, Y., Li, X., Yang, A., et al. (2022). "Spectacle lenses with aspherical lenslets for myopia control vs single-vision spectacle lenses: A randomized clinical trial." JAMA Ophthalmology, 140(5), 472-478. https://doi.org/10.1001/jamaophthalmol.2022.0401
  20. 51.Chamberlain, P., Peixoto-de-Matos, S.C., Logan, N.S., Ngo, C., et al. (2019). "A 3-year randomized clinical trial of MiSight lenses for myopia control." Optometry and Vision Science, 96(8), 556-567. https://doi.org/10.1097/OPX.0000000000001410 (144 enrolled, 109 completed, aged 8-12). Microbial keratitis with overnight orthokeratology was estimated at 13.9 per 10,000 patient-years in US children (95% CI 1.7-50.4): Bullimore, M.A., Sinnott, L.T., and Jones-Jordan, L.A. (2013). "The risk of microbial keratitis with overnight corneal reshaping lenses." Optometry and Vision Science, 90(9), 937-944. https://doi.org/10.1097/OPX.0b013e31829cac92
  21. 52.Zadnik, K., Schulman, E., Flitcroft, I., Fogt, J.S., et al. (2023). "Efficacy and safety of 0.01% and 0.02% atropine for the treatment of pediatric myopia progression over 3 years: A randomized clinical trial." JAMA Ophthalmology, 141(10), 990-999. https://doi.org/10.1001/jamaophthalmol.2023.2097 (576 children; the prespecified primary endpoint failed and 0.01% met secondary endpoints; sponsored by Vyluma); Repka, M.X., Weise, K.K., Chandler, D.L., Wu, R., et al. (2023). "Low-dose 0.01% atropine eye drops vs placebo for myopia control: A randomized clinical trial." JAMA Ophthalmology, 141(8), 756-765. https://doi.org/10.1001/jamaophthalmol.2023.2855 (187 US children; -0.82 versus -0.80 D). A clear dose-response appeared in Hong Kong: Yam, J.C., Jiang, Y., Tang, S.M., Law, A.K.P., et al. (2019). "Low-concentration atropine for myopia progression (LAMP) study." Ophthalmology, 126(1), 113-124. https://doi.org/10.1016/j.ophtha.2018.05.029 . As of March 2026 no atropine drop for myopia was approved in the United States, while Japan and the European Union had approved one: Novack, G.D. (2026). "Use of clinical pharmacology in slowing the myopia epidemic." Clinical Pharmacology & Therapeutics, 120(3), 592-593. https://doi.org/10.1002/cpt.70364
  22. 53.Lawrenson, J.G., Huntjens, B., Virgili, G., Ng, S., et al. (2025). "Interventions for myopia control in children: a living systematic review and network meta-analysis." Cochrane Database of Systematic Reviews, 2(2), CD014758. https://doi.org/10.1002/14651858.CD014758.pub3 (104 trials, 17,509 children; one-year slowing of 0.90 D for high-dose atropine at moderate certainty, 0.25 D for low-dose at very low certainty, 0.45 D for peripheral-plus spectacles at very low certainty; orthokeratology reduced axial growth by 0.18 mm at moderate certainty)
  23. 54.Chua, W.H., Balakrishnan, V., Chan, Y.H., Tong, L., et al. (2006). "Atropine for the treatment of childhood myopia." Ophthalmology, 113(12), 2285-2291. https://doi.org/10.1016/j.ophtha.2006.05.062 ; rebound after stopping in Tong, L., Huang, X.L., Koh, A.L., Zhang, X., et al. (2009). "Atropine for the treatment of childhood myopia: effect on myopia progression after cessation of atropine." Ophthalmology, 116(3), 572-579. https://doi.org/10.1016/j.ophtha.2008.10.020 . For prevention rather than control, two years of nightly 0.05% atropine cut myopia incidence to 28.4% against 53.0% on placebo, while 0.01% did not differ from placebo: Yam, J.C., Zhang, X.J., Zhang, Y., Yip, B.H.K., et al. (2023). "Effect of low-concentration atropine eyedrops vs placebo on myopia incidence in children: The LAMP2 randomized clinical trial." JAMA, 329(6), 472-481. https://doi.org/10.1001/jama.2022.24162
  24. 55.Ostrin, L.A., and Schill, A.W. (2026). "Safety evaluation of 4 red light therapy devices for myopia." JAMA Ophthalmology, 144(3), 255-258. https://doi.org/10.1001/jamaophthalmol.2025.5660 (two devices reached ANSI group 1 limits within 2.8 and 1.4 seconds for a 7 mm pupil, against a 180-second treatment time); efficacy in Jiang, Y., Zhu, Z., Tan, X., Kong, X., et al. (2022). "Effect of repeated low-level red-light therapy for myopia control in children: A multicenter randomized controlled trial." Ophthalmology, 129(5), 509-519. https://doi.org/10.1016/j.ophtha.2021.11.023 ; a case of retinal damage in Liu, H., Yang, Y., Guo, J., Peng, J., et al. (2023). "Retinal damage after repeated low-level red-light laser exposure." JAMA Ophthalmology, 141(7), 693-695. https://doi.org/10.1001/jamaophthalmol.2023.1548
  25. 56.National Eye Institute. Retinal detachment. https://www.nei.nih.gov/learn-about-eye-health/eye-conditions-and-diseases/retinal-detachment ("If you have symptoms of retinal detachment, go to your eye doctor or the emergency room right away"; extreme nearsightedness raises the risk)
  26. 57.Klepeis, N.E., Nelson, W.C., Ott, W.R., Robinson, J.P., et al. (2001). "The National Human Activity Pattern Survey (NHAPS): a resource for assessing exposure to environmental pollutants." Journal of Exposure Analysis and Environmental Epidemiology, 11(3), 231-252. https://doi.org/10.1038/sj.jea.7500165 (9,386 US respondents, 1992-1994: 87% of time in enclosed buildings and about 6% in enclosed vehicles)

This topic carries 57 notes in the research manuscript; the 26 above are those behind the material on this page. Full source register.