What Causes Myopia?
Genetics, Screens, and the Outdoor Factor
Short answer: Myopia is caused by a combination of genetic risk and environmental triggers — mainly too little outdoor time and too much near work at close distances. Neither factor alone explains the epidemic; both together drive it.
Genetics: the predisposition
Myopia runs in families. If one parent is myopic, the risk to a child is approximately double that of a child with no myopic parents. With both parents myopic, risk roughly quadruples. Specific genes associated with axial length and eye growth have been identified, though no single gene determines whether myopia develops.
However, genetics alone cannot explain the dramatic rise in myopia prevalence over the past 50 years. In 1960, approximately 20% of East Asian young adults had myopia. By 2020, that number was 80–90% in urban populations. Genetics don't change that fast — environment does.
The outdoor time factor
This is the most consistent and robust environmental finding in myopia research. Children who spend more time outdoors have significantly lower rates of myopia onset. The mechanism is primarily light intensity, not viewing distance: outdoor light (10,000–100,000 lux) triggers retinal dopamine release, which appears to regulate axial elongation. Indoor light (typically 300–500 lux) does not provide the same signal.
The threshold effect appears around 90–120 minutes of outdoor time per day. Studies in Taiwan and Australia found that adding 40 minutes of outdoor time per school day significantly reduced myopia onset rates over 1–2 years.
Near work and close viewing
Extended periods of close focusing — reading, homework, screen use at short distances — are associated with higher myopia rates. The proposed mechanism involves sustained contraction of the ciliary muscle and relative peripheral hyperopic defocus, which signals the eye to grow longer.
The 20-20-20 rule (every 20 minutes, look at something 20 feet away for 20 seconds) is commonly recommended, though evidence for its specific effect on myopia progression is limited. The more important intervention is increasing outdoor time and reducing total daily near-work hours.
Why the epidemic is accelerating
The combination of urbanisation (fewer outdoor spaces), academic pressure (more near-work hours), and digital entertainment (screens displacing outdoor play) has created the perfect conditions for rapid myopia prevalence growth. In dense East Asian cities where academic pressure begins early and outdoor time is limited, the effect is most dramatic.
Assess your child's myopia risk factors
The app asks about parental myopia, near-work hours, and outdoor time — and incorporates these into the overall risk score alongside axial length measurements.
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This page is for educational purposes and does not constitute medical advice. MyopiaTracker is a decision-support tool — not a diagnostic device. MiSight® is a registered trademark of The Cooper Companies. Stellest® is a registered trademark of Essilor International. MiyoSmart® is a registered trademark of Hoya Corporation. Treatment availability and regulatory approval vary by country. Consult a qualified optometrist or ophthalmologist for personalised advice.