What Causes Myopia in Children? The Risk Factors, Explained

If you’ve just found out your child is short-sighted, you may already have read our guide to what myopia actually is. The next question most parents ask is: what causes myopia in children, and could anything have been done differently? Childhood short-sightedness has been rising sharply for decades. Researchers now have a much clearer picture of why. It isn’t one single cause, it’s a combination of genetics and everyday lifestyle factors. Understanding both can help you make sense of your own child’s risk.

What Causes Myopia in Children: Four Key Risk Factors

Rates of childhood myopia have climbed steadily since the 1970s. Current projections suggest that by 2050, roughly half the world’s population could be short-sighted. That’s not just a story about more people needing glasses. Higher rates of myopia, especially high myopia, carry a greater long-term risk of serious eye conditions later in life.

Research points to four main contributors.

1. Genetics: One Cause of Myopia in Children

If one parent is myopic, a child is more likely to become myopic too. The risk rises further when both parents are short-sighted. Genetics isn’t the whole story, though. Two children with similar lifestyles and similar family backgrounds can have very different outcomes, because genetic susceptibility interacts with environment rather than acting alone.

2. Not Enough Time Outdoors

This is the factor researchers consistently point to as the single most protective one. Bright natural light appears to trigger a response in the retina that may help slow down the eye elongation that causes myopia. This effect looks strongest for preventing myopia from starting in the first place, rather than slowing it once it’s already present. Children who spend around two hours a day outdoors tend to have a meaningfully lower risk of developing myopia than those who don’t. The College of Optometrists’ evidence review covers the research behind this in more depth.

This matters practically: it’s less about restricting what children do indoors, and more about actively building outdoor time into the day.

3. Screen Time and Near Work

Screens get a lot of the blame, and there is a genuine association between heavy screen use and myopia risk. But the picture is more nuanced than “screens cause myopia.” Much of the effect seems to come from what screen time displaces, time spent outdoors. Add in the sheer amount of close-up focusing (near work) that reading, homework, and devices all involve, and the risk compounds. During COVID-19 lockdowns, when outdoor time dropped and screen time rose sharply worldwide, researchers observed faster myopia progression in children, a natural experiment that reinforced how closely these factors interact.

The practical takeaway isn’t necessarily “ban screens,” but rather balancing near work with regular breaks and outdoor time.

4. Urban Living and Environment

Children in cities tend to have higher rates of myopia than children in rural areas. This is likely down to a mix of reasons: less access to green space, more structured indoor schedules, and in some regions, long winters that limit outdoor time. None of these are things you can necessarily change, but they’re useful context if you’re wondering why myopia rates vary so much between areas.

What This Means for Parents

None of these risk factors guarantee a child will or won’t develop myopia, but knowing what causes myopia in children helps you spot it early, which matters. The earlier myopia starts, the faster it tends to progress, and the more valuable early monitoring becomes. Practical steps worth considering:

• Aim for regular outdoor time, ideally in the region of two hours a day
• Encourage breaks during long stretches of reading, homework, or screen use
• Book regular eye tests, especially if either parent is short-sighted
• If your optician confirms a prescription, ask specifically about myopia management options rather than only a standard pair of glasses

Next Steps

If your child has recently been diagnosed with myopia, or their prescription keeps increasing, it’s worth understanding what treatment options actually exist beyond a standard lens upgrade. Our guide to myopia control lenses covers spectacle lenses, contact lenses, and orthokeratology, and how to find an optician that offers them.

This post is for general information only and isn’t a substitute for professional advice. Speak to a registered optometrist about your child’s individual risk and eye health.