Why Myopia Is Rising Around the World: Causes and Risks

Not long ago, wearing glasses for distance vision was something only a minority of children needed. Today, in some cities in East Asia, the large majority of young adults finishing school are nearsighted, and rates are rising in Europe, North America and elsewhere too. Researchers increasingly use the word epidemic to describe the trend, not because myopia is contagious, but because of how rapidly and widely it is spreading.

Why is this happening, and does it matter if glasses can correct it? In this article we look at the numbers, the main causes identified by research, the role of genetics, and the reasons eye doctors are concerned about high myopia in particular. Understanding the causes is also the key to prevention, especially for children.

What is myopia?

In a normal eye, light from distant objects is focused precisely onto the retina, the light-sensitive layer at the back of the eye. In myopia, the eye is usually too long from front to back (axial myopia), or less commonly the cornea is too steeply curved. Light from distant objects comes to a focus in front of the retina, so far objects look blurry while near objects remain clear.

Myopia usually begins in childhood, typically between about 6 and 12 years of age, and tends to progress as the child grows, often stabilising in the late teens or early twenties. The earlier it starts, the more time it has to progress, and the higher the final prescription is likely to be. Myopia is measured in dioptres; high myopia is commonly defined as -6.00 dioptres or more. For a broader overview of how vision problems like this work, see our guide on refractive errors.

How fast is myopia rising?

The best-known global estimate comes from a 2016 analysis published in the journal Ophthalmology by Brien Holden and colleagues, which pooled data from many population studies. They estimated that about 1.4 billion people, around 23% of the world's population, were myopic in 2000. Based on trends, they projected this would rise to almost 5 billion people, about half of the world's population, by 2050. They also estimated that the number of people with high myopia would increase roughly fivefold over the same period, to nearly a billion, or around 10% of the global population.

Figures based on Holden et al., Ophthalmology, 2016. Projections depend on assumptions and may change as prevention efforts take effect.

The East Asian experience

The change is most striking in urban East and Southeast Asia, including China, Hong Kong, Taiwan, Japan, South Korea and Singapore. Studies of young adults in some of these places have found that the large majority, in some cohorts well over 80%, are myopic by the end of schooling, and a significant minority have high myopia. Only a few generations ago, rates in the same populations were much lower. Such a rapid shift within populations whose genetic makeup has not changed points strongly to environmental causes.

Other regions

Rates are also rising in Europe and North America, though generally from a lower base. Studies comparing data from different decades in the United States and parts of Europe have found substantial increases in myopia prevalence, particularly in younger generations and among those with more years of education. In many lower-income countries, rates are rising as urbanisation and schooling expand.

Cause one: intensive near work and education

One of the most consistent findings in myopia research is a link between education and myopia. People who spend more years in education, and children in highly competitive schooling systems with long hours of study and homework, are more likely to be myopic. Studies using genetic methods (Mendelian randomisation) have suggested that more years of education may actually cause more myopia, rather than simply being associated with it.

Near work, such as reading, writing and using screens at close distance, is thought to be part of the explanation. Meta-analyses have found that more time spent on near activities is associated with a higher risk of myopia. Very close working distances and long, uninterrupted sessions appear to carry particular risk. The exact biological mechanism is not fully understood. One theory concerns the way the image falls on the peripheral retina during close focus, which may send a signal to the eye to grow longer.

Digital devices have added to the total amount of near work in many children's lives. Whether screens are worse than books is still debated, but phones are often held very close and used for long periods, and screen time frequently replaces outdoor play. Our article on screen time and children's eyes gives practical guidance for families.

Cause two: too little time outdoors

The second major factor, and perhaps the most important from a prevention point of view, is lack of daylight. Numerous studies have found that children who spend more time outdoors are less likely to become myopic, regardless of how much near work they do. Randomised trials in schools in China and Taiwan, in which children were given extra outdoor time during the school day, found fewer new cases of myopia in the intervention groups.

The leading explanation is light intensity. Outdoor light is typically many times brighter than indoor lighting, even on cloudy days. Bright light is thought to stimulate the release of dopamine in the retina, which acts as a signal that slows the elongation of the eyeball. Animal experiments support this idea. Other features of outdoor environments, such as the wider range of viewing distances and the spectrum of daylight, may also contribute. Read more in our article on outdoor time as a shield against childhood myopia and our guide on daylight and vision.

Cause three: genetics

Genes do matter. Children with one myopic parent are more likely to become myopic than those with none, and the risk is higher still if both parents are myopic. Large genetic studies have identified hundreds of gene variants associated with refractive error, many of them related to how the eye grows in response to visual signals.

However, genetics cannot explain the speed of the recent rise. Gene pools do not change significantly in two or three generations. The best current understanding is that genes influence how susceptible an individual is, while environment determines how much of that susceptibility is expressed. A child with a genetic tendency to myopia who spends a lot of time indoors doing close work is at particularly high risk. Family history also influences risk for other eye conditions, as our article on family history and eye disease explains.

Why high myopia is a serious concern

If glasses, contact lenses or laser surgery can correct the blur, why worry? The problem is that myopia, especially high myopia, is not just an optical issue. A longer eye is a stretched eye. The retina, the choroid beneath it and the sclera (the white outer wall) all become thinner, and this stretching increases the risk of several sight-threatening conditions later in life. Correcting the blur does not remove these risks, and laser surgery does not change the length of the eye.

Retinal detachment

The thinner, stretched retina in a highly myopic eye is more prone to tears and holes, which can lead to retinal detachment, where the retina peels away from the back of the eye. This is a medical emergency that needs prompt surgery to prevent permanent vision loss. The risk increases substantially with the degree of myopia.

Myopic maculopathy

Myopic maculopathy (also called pathological myopia or myopic macular degeneration) involves degenerative changes at the macula, the central part of the retina responsible for detailed vision. It can include thinning and atrophy, breaks in the layer beneath the retina, and the growth of abnormal blood vessels (myopic choroidal neovascularisation). In parts of East Asia, myopic maculopathy has become one of the leading causes of irreversible visual impairment. Some complications, such as abnormal blood vessels, can be treated with injections into the eye, but atrophy cannot be reversed.

Glaucoma and cataract

Myopia is also associated with a higher risk of open-angle glaucoma and with earlier development of certain types of cataract. These risks rise with the degree of myopia, which is why people with high myopia benefit from regular eye examinations throughout life, including a dilated look at the retina.

What can be done

The rise of myopia is not inevitable. Prevention and treatment strategies now have a solid evidence base:

• Outdoor time: around two hours of daylight a day is commonly recommended for children to reduce the risk of developing myopia.
• Healthy near work habits: regular breaks, a reading distance of at least about 30 cm, good lighting and limits on recreational screen time.
• Myopia control treatments: for children who already have myopia, eye care professionals may recommend low-dose atropine eye drops, special myopia control spectacle lenses, myopia control soft contact lenses or orthokeratology. Trials such as LAMP in Hong Kong have shown that low-dose atropine can slow progression. The choice of treatment and any medication are decided by the eye doctor.
• Early detection: regular eye checks for children, especially those with myopic parents, allow early treatment.

Eye exercises, unfortunately, are not among the solutions: they do not prevent or reverse myopia. They can, however, make close work more comfortable as part of good break habits.

When to see a doctor

Children should have their vision checked regularly, and sooner if they squint, sit close to screens, struggle to see the board or have myopic parents. Adults with myopia, particularly high myopia, should have regular eye examinations including a check of the retina, and should know the warning signs of retinal detachment.