Near-sightedness facts for kids

Kids Encyclopedia Facts

Quick facts for kids Near-sightedness
Synonyms	short-sightedness, myopia

Diagram showing changes in the eye with near-sightedness
Symptoms	Distant objects appear blurry, close objects appear normal, headaches, eye strain
Complications	Retinal detachment, cataracts, glaucoma
Causes	Combination of genetic and environmental factors
Risk factors	Near work, greater time spent indoors, family history
Diagnostic method	Eye examination
Prevention	Unknown
Treatment	Eyeglasses, contact lenses, surgery
Frequency	1.5 billion people (22%)

Near-sightedness, also called myopia or short-sightedness, is a common eye condition. It happens when your eye focuses light in front of your retina instead of directly on it. This makes faraway objects look blurry, while close-up things appear clear. You might also get headaches or eye strain if you are near-sighted.

Myopia occurs because your eyeball grows a bit too long. Sometimes, the lens inside your eye might be too strong. It's a type of refractive error, which means your eye doesn't bend light correctly. An eye examination can tell if you have it.

Spending more time outdoors, especially for young children, might help lower the risk of becoming near-sighted. This could be because of natural light. You can correct near-sightedness with eyeglasses, contact lenses, or refractive surgery. Eyeglasses are the easiest and safest way to see clearly. Contact lenses offer a wider view but can increase the risk of eye infections. Surgeries like LASIK change the shape of your cornea permanently.

Near-sightedness is a very common eye problem. About 1.5 billion people worldwide have it. That's about 22% of everyone! The number of people with myopia has grown since the 1950s. If not corrected, near-sightedness is a major cause of blurry vision around the globe.

What is Myopia?

The word myopia comes from ancient Greek words. It means "short-sight" or "to shut the eyes." This refers to how some near-sighted people might squint to see better. The opposite of myopia is hyperopia, or far-sightedness.

How Do You Know if You Are Near-Sighted?

Human eyesight two children and ball with myopia

Near-sighted vision (top/left) compared to normal vision (bottom/right).

If you are near-sighted, objects far away will look blurry. You can see clearly only up to a certain distance. If your myopia is very strong, even reading up close might be hard. Most near-sighted eyes look normal during a check-up.

Myopia often starts when kids are in school. It can get worse between the ages of 8 and 15.

What Causes Near-Sightedness?

Scientists believe near-sightedness comes from a mix of your genes and your environment. Things that increase your risk include:

Doing lots of close-up work, like reading or using screens.
Spending more time indoors.
Living in cities.
Having family members who are near-sighted.

It's also linked to higher education levels. While many ideas have been explored, no single cause has been strongly proven. However, studies of twins show that genes play a part. The rapid increase in myopia worldwide suggests that environmental factors are also very important.

Genes and Myopia

You can inherit a risk for myopia from your parents. Scientists have found many gene areas linked to myopia. It's not just one gene, but a complex mix of many genes working together. These genes might affect how your eye grows and develops.

Studies show that genes account for 60-90% of how much your vision changes. But the genes found so far only explain a small part of myopia cases. This means there are many more genes yet to be discovered.

Environmental Factors

Environmental factors that increase the risk of near-sightedness include:

Not enough light exposure.
Low physical activity.
Lots of close-up work.
More years of schooling.

One idea is that not getting enough "normal" visual signals causes the eyeball to develop incorrectly. "Normal" means the kind of environment our eyes evolved for. Modern humans spend a lot of time indoors. This might put them at risk for myopia.

Children who spend more time doing physical exercise and playing outdoors have lower rates of myopia. This suggests that the varied sights and activities outside help prevent it. Being exposed to daylight for long hours might help by increasing a chemical called dopamine in the eye.

Myopia can also be caused by wearing glasses that are too strong. This is why eye doctors use special tests to make sure your prescription is just right.

Near-sightedness is also more common in children with certain health conditions. These include diabetes, childhood arthritis, and systemic lupus erythematosus.

How Does Myopia Work?

Myopia is like a camera that's out of focus. The light entering your eye focuses too soon.

Axial myopia means your eyeball is too long from front to back.
Refractive myopia means the parts of your eye that bend light, like the cornea or lens, are too curved or too strong.

If your pupil (the black center of your eye) is large, your blurry vision might seem worse. If it's small, your vision might seem clearer. This is why some people with myopia have trouble seeing in dim light.

How is Myopia Diagnosed?

An eye care professional, like an optometrist or ophthalmologist, usually diagnoses myopia. During an eye exam, they use special tools. An autorefractor or retinoscope gives an initial idea of your vision. Then, a phoropter helps them fine-tune your eyeglass prescription. Other common vision problems are hyperopia (far-sightedness) and astigmatism (blurry vision at all distances).

Types of Myopia

Myopia can be described in different ways:

Simple myopia: This is the most common type. It's usually not very strong, less than -6.00 diopters.
Degenerative myopia: Also called pathological myopia. This is a more serious form where the eye changes a lot. It gets worse over time and can cause significant vision problems.
Pseudomyopia: This is temporary blurry vision. It happens when your eye muscles get "stuck" trying to focus up close.
Nocturnal myopia: Your vision might be blurry at night or in low light.
Nearwork-induced transient myopia (NITM): Short-term blurry vision after doing a lot of close-up work.
Induced myopia: This can be caused by certain medicines, high glucose levels, or other health issues. For example, high blood sugar can make your eye's lens swell, causing temporary myopia.

How Strong is Myopia?

The strength of your myopia is measured in diopters.

Low myopia: Between -0.50 and -3.00 diopters.
Moderate myopia: Between -3.00 and -6.00 diopters. People with moderate myopia might have a higher risk of glaucoma.
High myopia: -6.00 diopters or more. People with high myopia have a higher risk of serious eye problems. These include retinal detachment, glaucoma, and macular degeneration. They might also see more floaters (small spots or lines in their vision).

When Does Myopia Start?

Myopia can also be grouped by when it begins:

Congenital myopia: Present at birth.
Youth onset myopia: Starts in childhood or teenage years. The eye's power can change until about age 21.
School myopia: Appears during school years. This is often linked to lots of close-up reading and studying.
Adult onset myopia: Starts after age 20.

Can Myopia Be Prevented?

Scientists are still studying ways to slow down or prevent myopia from getting worse. Many studies have had mixed results. Eye drops are a common approach used by eye specialists. Spending more time outdoors is also suggested to protect young children from myopia. Some doctors also advise spending less time on close-up work.

Glasses and Contacts for Prevention

Wearing reading glasses for close work might help by reducing the need for your eyes to focus hard. Some special contact lenses have also been approved to help slow down myopia in children. These lenses aim to focus light in a way that prevents the eye from growing too long.

Medication

Certain eye drops, like atropine drops, can slow down myopia in children under 18. These treatments can make your eyes sensitive to light or blur your near vision.

Other Methods

Scleral reinforcement surgery is a procedure that adds support to the back of the eye. This helps prevent the eye from stretching further in severe cases.

How is Myopia Treated?

Glasses are commonly used to address near-sightedness.

The most common treatment for myopia is wearing glasses or contact lenses. These help your eye focus light correctly onto the retina. Other treatments include special contact lenses worn overnight (orthokeratology) and refractive surgery.

Compensating for myopia using a corrective lens.

Glasses and Contacts

Corrective lenses bend the light entering your eye. This makes sure the image lands perfectly on your retina. The strength of the lens is measured in diopters. Near-sighted people need lenses with negative diopter numbers. The stronger your myopia, the higher the negative number.

Strong glasses can sometimes cause slight distortions or color fringes. Contact lenses usually avoid these issues because they move with your eye.

Surgery

Refractive surgery changes the shape of your cornea or places an extra lens inside your eye.

Photorefractive Keratectomy (PRK)

PRK uses a laser to remove a tiny amount of tissue from the surface of your cornea. This reshapes it to correct your vision. PRK is safe for mild to moderate myopia. The recovery can be a bit painful.

LASIK

In LASIK, a thin flap is made on your cornea. A laser then reshapes the tissue underneath. After the laser, the flap is put back. LASIK is usually painless and has a quick recovery. However, there can be risks like flap problems or weakening of the cornea.

Phakic Intra-Ocular Lens (IOL)

This surgery involves putting an extra lens inside your eye, in front of your natural lens. It doesn't change your cornea. While it can give good vision, it has risks like glaucoma or cataracts.

Orthokeratology (Ortho-K)

Ortho-K uses special rigid contact lenses worn overnight. These lenses temporarily reshape your cornea while you sleep. This allows you to see clearly during the day without glasses or contacts. Ortho-K can correct myopia up to -6 diopters. It can also help slow down myopia progression. Risks include eye infections.

Intrastromal Corneal Ring Segment (ICRS)

ICRS involves placing small plastic rings inside the cornea. These rings help flatten the cornea to correct myopia. They are also used to treat a condition called keratoconus.

Alternative Treatments

Some alternative therapies claim to improve myopia. These include eye exercises or relaxation techniques. However, scientific studies have not found clear evidence that these methods work to treat near-sightedness. They are not recommended by eye doctors.

How Common is Myopia?

Myopia affects a huge number of people worldwide. The number of people with myopia varies a lot by age, country, and other factors.

In some parts of Asia, myopia is very common, affecting 70-90% of people.
In Europe and the United States, about 30-40% of adults have myopia.
In Africa, it's less common, affecting 10-20% of people.

Myopia is about twice as common in Jewish people compared to non-Jewish people. It's also less common in people of African descent.

Myopia in Asia

Myopia is especially common in some Asian countries.

Singapore might have the highest rate, with up to 80% of people being near-sighted.
In China, about 400 million people have myopia. In high schools, 77% of students are near-sighted.

Myopia in Europe

In the United Kingdom, about 50% of university students are near-sighted.
In Western Europe, about 27% of adults over 40 have at least -1.00 diopters of myopia.

Myopia in North America

Myopia has increased a lot in the United States in recent decades.

In the early 1970s, about 25% of Americans aged 12-54 were near-sighted.
By the early 2000s, this number climbed to 42%.
Among children in grades 1-8, about 9% have myopia. Asian children have the highest rates (19%), followed by Hispanic children (13%).

Myopia in Australia

In Australia, about 17% of people overall have myopia. Among children aged 4-12, about 8% are near-sighted.

Myopia in South America

In Brazil, a 2005 study found that 6% of people aged 12-59 had myopia.

History of Myopia

The ancient Greek thinker Aristotle noticed the difference between near-sighted and far-sighted people. The Greek-Roman doctor Galen first used the term "myopia." The first glasses to correct myopia were invented in Germany in 1451.

In 1604, Johannes Kepler was the first to explain that near-sightedness happens because light focuses in front of the retina. He also showed that concave lenses could correct it. Later, in 1632, Vopiscus Fortunatus Plempius confirmed that myopia was due to the eyeball being too long.

Myopia in Society

The words "myopia" and "myopic" are sometimes used to describe thinking that is narrow or doesn't consider the future. It means someone might focus only on what's happening now, without thinking about long-term effects. For example, a "myopic decision" might be good for today but bad for tomorrow.

Myopia and Other Factors

Studies have found links between myopia and intelligence or school success. However, it's not clear if one causes the other. Myopia is also linked to small, quick eye movements called microsaccades. This suggests that blurry vision might affect how your eyes move.