Glossary
Myopia
Nearsightedness, produced by an eyeball grown too long. It affects 80 to 90% of school-leavers in East Asia, and outdoor time in childhood roughly halves the rate of new cases.
Published Updated
Chapters of the book that mention Myopia
Where this comes from
In the reference topic that owns this term
Reference topic 24, The Indoor Eye, states the mismatch as a card: what the system evolved to expect, what it gets instead, and what happens in the gap.
Mismatch card
- 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.
- What happens in the gap
The eye overgrows, distance blurs for good, and a stretched retina carries lifelong risk.
What that chapter recommends
3 of the 5 graded recommendations in Reference topic 24, strongest evidence first. How the grades work.
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.Two hours was Taiwan's school target and is widely endorsed. China's plan specifies one to two, and the US National Academies at least one. Shade and cloud count: benefit appeared from 1,000 lux.
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, an eye examination before first grade, and sooner if a child squints at distance.
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.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.
Related terms
Graded recommendations elsewhere that mention Myopia
- Outdoors as the default settingEvidence grade: Probable. Good observational evidence with a plausible mechanism, or small or few trials.Topic 34
The argument behind this term, its studies and its notes are in Reference topic 24 of the reference library. The book gives the practical version. Get the book.