Myopia, or nearsightedness, develops when a child’s eyeball grows too long from front to back, causing distant objects to blur while close-up vision stays sharp. About 30% of children and adolescents worldwide are now myopic, a prevalence that has climbed from roughly 24% in 1990 to nearly 36% today. The causes are a mix of genetics, environment, and daily habits, and understanding each one helps explain why rates keep rising and what parents can actually do about it.
How the Eye Physically Changes
In a normally developing eye, the distance from the front surface to the retina at the back (called axial length) reaches about 23 mm in girls and 23.5 mm in boys by the time growth stops in the early teens. During school age, a healthy eye grows roughly 0.1 to 0.2 mm per year, slowing after age 10 and eventually stopping.
In children who develop myopia, that growth accelerates. Eye elongation speeds up in the year before a child becomes nearsighted, reaching about 0.2 mm per year. Once myopia sets in, the rate jumps to more than 0.3 mm per year until around age 10 or 11, then slows to about 0.2 mm per year through the teen years. By the time things stabilize, the average myopic eye measures around 25 mm in girls and 25.5 mm in boys. Because the eyeball is too long, light focuses in front of the retina instead of on it, and distance vision blurs.
That extra length matters beyond just needing glasses. Eyes that stretch past 26 mm face dramatically higher odds of serious problems in adulthood, including retinal detachment, glaucoma, and a type of degeneration at the back of the eye. If axial length reaches 30 mm or more, there is a 90% chance of significant vision impairment over a lifetime. This is why eye care professionals increasingly focus on slowing eye growth in childhood, not just correcting blurry vision with lenses.
The Role of Genetics
A child’s family history is one of the strongest predictors of myopia. Data from the Hong Kong Children Eye Study illustrates this clearly: among children whose parents were both non-myopic, the prevalence of myopia was about 10.5%. With one mildly myopic parent, it rose to roughly 12%. When both parents had mild myopia, it climbed to nearly 18%. And among children with two moderately myopic parents, prevalence exceeded 40%, reaching as high as 54% in the most affected combinations.
The pattern is dose-dependent. The more severe each parent’s myopia, the higher the child’s risk. This doesn’t mean myopia is inevitable for these children, but it does mean the eye has a stronger biological tendency toward elongation. Genetics set the stage; environment determines how far it goes.
Near Work and Reading Distance
When children spend extended time focusing on nearby objects, whether books, tablets, homework, or phones, their eyes must constantly adjust to keep the close image sharp. This sustained effort is thought to trigger signals within the eye that promote elongation. It’s the total volume of near work throughout the day, not any single activity, that drives the risk.
How close a child holds their reading material also matters. Children who habitually read at less than 20 cm (about 8 inches) from their eyes are roughly 67% more likely to be myopic compared to those who read at 30 cm (12 inches) or more. That’s a meaningful difference from something as simple as posture and distance. Encouraging your child to hold books and screens at arm’s length, or at least past the 30 cm mark, is one of the easiest protective steps available.
A common question is whether screens are worse than books. The honest answer is that the evidence does not clearly separate the two. Both involve sustained close focus, and both contribute to the same elongation signals. The real issue is cumulative time spent on all near-work tasks combined, and in many children’s lives today, screens have simply added hours of close focus on top of the reading and homework that were already there.
Outdoor Time and Light Exposure
One of the most consistent findings in myopia research is that children who spend more time outdoors develop myopia less often and progress more slowly if they already have it. The protective effect appears to come from exposure to bright natural light, which stimulates the release of a chemical messenger in the retina called dopamine. Dopamine acts as a brake on eye elongation, helping regulate normal growth.
Indoor lighting, even in a well-lit room, typically reaches only 300 to 500 lux. Outdoor light on an overcast day delivers around 10,000 lux, and direct sunlight can exceed 100,000 lux. The difference is enormous, and the eye responds to it. Most guidelines now recommend children spend at least 90 minutes to two hours outdoors daily. The exact optimal dose is still being refined, but the direction is clear: more outdoor time is protective, and it works even for children with a strong family history of myopia.
Importantly, the benefit comes from being outside in daylight, not from physical exercise itself. A child reading on a park bench in bright light gets more protective benefit than a child playing in a dimly lit gymnasium.
Why Rates Are Rising So Quickly
Projections estimate that by 2050, nearly 40% of children and adolescents globally will be myopic, with total cases exceeding 740 million. Genetics haven’t changed in a generation, so the explanation lies almost entirely in how children’s daily lives have shifted. More years of intensive education, more hours of close-focus screen use, and less unstructured outdoor play have created an environment that pushes genetically susceptible eyes toward elongation.
East Asian countries, where academic demands are especially intense and outdoor play time is limited, have seen the most dramatic increases. In parts of China, South Korea, and Singapore, myopia rates among teenagers exceed 80%. But the trend is global. Rates are climbing in Europe, North America, and South America as well, tracking alongside increased near-work hours and decreased outdoor time across cultures.
Options for Slowing Progression
Because the physical changes in myopia are permanent (a stretched eye doesn’t shrink back), the focus for children already showing signs is on slowing further elongation. Several approaches have good evidence behind them.
Specialty Contact Lenses
Orthokeratology lenses are rigid lenses worn overnight that temporarily reshape the cornea, providing clear vision during the day without glasses. They also slow axial elongation. In a two-year comparison, children wearing these lenses showed 0.41 mm of eye growth, versus 0.65 mm in children wearing standard glasses. That’s a reduction of roughly 37% in how much the eye elongated. Multifocal soft contact lenses, worn during the day, work through a different optical design but achieve a similar slowing effect.
Atropine Eye Drops
Low-concentration atropine drops, used nightly, reduce the signals that drive eye elongation. Studies comparing various concentrations have found that higher doses (0.05% and above) provide greater slowing of progression, while very low doses like 0.01% offer less benefit than initially hoped. Your child’s eye care provider can help weigh the trade-offs, since higher concentrations cause more light sensitivity and near-vision blur during treatment.
Lifestyle Changes
Increasing outdoor time, taking regular breaks from near work (the “20-20-20” guideline suggests looking at something 20 feet away for 20 seconds every 20 minutes), and maintaining reading distances of at least 30 cm all contribute to slowing progression. These behavioral changes work alongside optical or pharmaceutical treatments and are worth adopting regardless of which other interventions a family chooses.
What Age Matters Most
Myopia that begins earlier tends to progress further, simply because there are more years of eye growth ahead. A child who becomes nearsighted at age 6 will typically reach a higher final prescription than one who develops myopia at 12. This is why early detection matters. Children don’t always report blurry distance vision, especially if they’ve never known anything different. Regular eye exams starting before school age can catch the first signs, including changes in axial length, before a child even needs glasses. The earlier intervention begins, the more total elongation can be prevented over the growing years.