Short-sightedness (myopia) usually occurs when the eyes grow slightly too long, which means they're unable to produce a clear image of objects in the distance.

It's not clear exactly why this happens, but it's thought to be the result of a combination of genetic and environmental factors that disrupt the normal development of the eye.

How the eye works

Light passes through the cornea (the transparent layer at the front of the eye) and into the lens (the transparent structure that sits behind the cornea).

This focuses it on to the retina (a layer of light-sensitive tissue at the back of the eye) to create an image that's then sent to the brain.

To produce a perfectly clear image, the cornea should be evenly curved and the eye needs to be the right length. 

In people with short-sightedness, the eye has usually grown slightly too long.

This means that when you look at distant objects, the light isn't focused directly on to your retina, but a short distance in front of it.

This results in a blurry image being sent to your brain.

What can increase your risk?

Although it's not clear exactly why some people become short-sighted, there are some things that can increase your chances of developing the condition.

Your genes

Short-sightedness is known to run in families, so you're more likely to develop it if one or both or your parents are also short-sighted.

Research has so far identified more than 40 genes linked to short-sightedness.

These are responsible for the eye's structure and development, and signalling between the brain and the eyes.

Too little time outdoors

Research has found that spending time playing outside as a child may reduce your chances of becoming short-sighted, and existing short-sightedness may progress less quickly.

This may be related to light levels outdoors being much brighter than indoors.

Both sport and relaxation outdoors appear to be beneficial in reducing the risk of short-sightedness.

Excessive close work

Spending a lot of time focusing your eyes on nearby objects, such as reading, writing and possibly using hand-held devices (phones and tablets) and computers can also increase your risk of developing short-sightedness.

An "everything in moderation" approach is therefore generally recommended.

Although children should be encouraged to read, they should also spend some time away from reading and computer games each day doing outdoor activities.

You can find out if you have short-sightedness (myopia) by having an eye test at your local opticians.

Find an opticians near you

You should have a routine eye test at least every 2 years, but you can book a test at any point if you have any concerns about your or your child's vision.

For some people, such as children under 16 or those under 19 and in full-time education, eye tests are available free of charge on the NHS.

Read about NHS eyecare entitlements to check if you qualify.

What happens during an eye test

Your eyes will usually be tested by an optometrist (someone who's been specially trained to examine the eyes).

It can be difficult to examine young children's eyes, so they may sometimes need to be referred to a local hospital eye service for an eye test.

They may also need eye drops to dilate the pupil of the eye to get accurate measurements.

A number of different tests will usually be carried out as part of your eye test.

These may include:

• measurements of the pressure inside your eyes
• checks to measure how well your eyes work together
• visual acuity tests where you're asked to read from a chart that has rows of letters that get smaller on each line
• retinoscopy where a bright light is shone into your eye to see how it reacts

If the tests detect a possible problem with your distance vision, you may be asked to repeat the visual acuity tests while different strength lenses are placed in front of your eyes.

This will help the optometrist to determine what your glasses prescription should be.

Understanding your glasses prescription

If an eye test finds that you're short-sighted, you'll be given a prescription that describes what lenses you need to improve your vision.

This can be used to make glasses or contact lenses.

Your prescription will usually consist of 3 main numbers for each eye.

These are:

• Sph (sphere) – a positive number here indicates that you're long-sighted, while a negative number indicates that you're short-sighted
• Cyl (cylinder) – this number indicates whether you have astigmatism (where the front of your eye isn't perfectly curved)
• Axis – this describes the angle of any astigmatism you have

If you're short-sighted, the Sph number is the most relevant. This is given in a measurement called dioptres (D), which describes how severely short-sighted you are.

A score of -0.5D to -3D is usually considered to be mild myopia, while a score of more than -6D is considered to be severe or high myopia.

Glasses or contact lenses are the most common method of correcting short-sightedness (myopia). Laser surgery is also becoming increasingly popular.

Implanting artificial lenses in the eyes is a fairly new technique that's used very occasionally if laser surgery is ineffective or not possible (for example, people with very severe short-sightedness).

Corrective lenses

Glasses

Short-sightedness can usually be corrected using glasses made specifically to your prescription.

See diagnosing short-sightedness for more information about what your prescription means.

Wearing a lens made to your prescription will ensure light is focused onto the back of your eye (retina) correctly so distant objects don't appear as blurry.

The thickness and weight of the lenses you need will depend on how short-sighted you are.

Your eyesight often changes as you get older, which means you may eventually need to use 2 pairs of glasses: 1 pair for close vision activities such as reading, and the other pair for distance vision activities, such as watching television.

Some people prefer to use bifocal lenses that allow them to see objects clearly that are both close up and far away without changing their glasses.

You can also get multifocal lenses that help you see nearby objects and those at middle and long distances (varifocal glasses).

Contact lenses

Contact lenses can also be used to correct vision in the same way as glasses.

Some people prefer contact lenses to glasses because they're lightweight and almost invisible, but some people find them more of a hassle than wearing glasses.

Contact lenses can be worn on a daily basis and discarded each day (daily disposables), or they can be disinfected and reused.

They can also be worn for a longer period of time, although eye specialists generally recommend that contact lenses aren't worn overnight because of the risk of infection.

Some opticians very occasionally use a technique called orthokeratology. 

This involves wearing a hard contact lens overnight to flatten the curvature of the cornea (the transparent layer at the front of the eye) so you can see better without a lens or glasses during the day.

It's not a cure for short-sightedness because the cornea usually returns to its normal shape, but it may reduce reliance on lenses for some people.

Your optician can advise you about the most suitable type of contact lenses for you.

If you decide to wear contact lenses, it's very important that you keep your lenses clean and hygienic to prevent eye infections.

Read more about contact lens safety.

Availability and cost

You can get vouchers towards the cost of glasses or contact lenses if you're eligible (for example, if you're under 16 years of age or you receive Income Support).

Read about NHS eyecare entitlements to check if you qualify.

If you're not eligible, you'll have to pay for glasses or contact lenses. The cost of glasses can vary significantly depending on your choice of frame.

Entry-level glasses start at around £50, with designer glasses costing several hundred pounds.

The cost of contact lenses will vary, depending on your prescription and the type of lens you choose. 

They can range from £5 to £10 a month for some monthly disposables, to £30 to £50 a month for some daily disposables.

Laser eye surgery

Laser eye surgery involves using a laser to burn away small sections of your cornea to correct the curvature so light is better focused onto your retina.

There are 3 main types of laser eye surgery:

• photorefractive keratectomy (PRK) – where a small amount of the cornea's surface is removed, and a laser is used to remove tissue and change the shape of the cornea
• laser epithelial keratomileusis (LASEK) – similar to PRK, but involves using alcohol to loosen the surface of the cornea so a flap of tissue can be lifted out of the way, while a laser is used to alter the shape of the cornea; the flap is then put back in place afterwards
• laser in situ keratectomy (LASIK) – similar to LASEK, but a smaller flap of cornea is created

These procedures are usually carried out on an outpatient basis, so you won't normally have to stay in hospital overnight.

The treatment usually takes less than 30 minutes to complete and a local anaesthetic is used to numb your eyes while it's carried out.

Which procedure is best?

All 3 laser eye surgery techniques produce similar results, but they tend to have different recovery times.

LASEK or LASIK are usually the preferred methods as they cause almost no pain and your vision will usually start to recover within a few hours or days. But your vision may not fully stabilise for up to a month.

PRK can be a bit painful and it can take several months for your vision to stabilise afterwards.

LASIK can only be carried out if your cornea is thick enough. If your cornea is thin, the risk of complications occurring, such as loss of vision, is too high.

LASEK and PRK may be possible if your cornea isn't thick enough for LASIK.

The Royal College of Ophthalmologists has published a patient's guide to refractive laser surgery (PDF, 364kb) and also has answers to specific questions about laser refractive surgery (PDF, 196kb).

You can also read guidance from the National Institute for Health and Care Excellence (NICE) about laser surgery for the correction of refractive errors.

Results

The results of all 3 techniques are usually good.

While it may not always be possible to completely cure your short-sightedness, around 9 out of 10 people experience a significant improvement in their vision.

Many people are able to meet the minimum vision requirements for driving.

Most people who have laser surgery report that they're happy with the results.

But it's important to realise that laser surgery may not necessarily improve your vision to the same degree as wearing corrective lenses.

Also, as with any type of surgery, laser surgery carries the risk of complications.

Risks and complications

Laser eye surgery does carry risks, including:

• dry eyes – this will usually last a few months, during which time you can lubricate your eyes with special eye drops
• removal of too much cornea tissue – this occurs in around 1 in 20 cases and could leave you with an eye that's long-sighted
• reduced night vision – this usually passes within 6 weeks
• haze effect around bright lights – this will usually pass within 6 to 12 months

There's also a small risk of potentially serious complications that could threaten your vision, such as the cornea becoming too thin or infected.

But these problems are rare, occurring in less than 1 in every 500 cases.

Make sure you understand all the risks involved before deciding to have laser eye surgery.

Who can't have laser surgery?

You shouldn't have any sort of laser eye surgery if you're under the age of 21. This is because your vision may still be developing at this stage.

Even if you're over 21, laser eye surgery should only be carried out if your glasses or contact lens prescription hasn't changed significantly over the last 2 years or more.

You may also not be suited to laser surgery if you:

• have diabetes – this can cause abnormalities in the eyes that can be made worse by laser surgery to the cornea
• are pregnant or breastfeeding – your body will contain hormones that cause slight fluctuations in your eyesight, making precise surgery difficult
• have a condition that affects your immune system, such as HIV or rheumatoid arthritis (these conditions may affect your ability to recover after surgery)
• have other problems with your eyes, such as glaucoma (increased pressure in the eye) or cataracts (cloudy patches in the lens of the eye)

Laser eye surgery can generally be effective for people with a prescription of up to -10D.

Find out more about diagnosing short-sightedness

If your short-sightedness is more severe, lens implants may be more appropriate.

Availability and cost

Laser surgery isn't usually available on the NHS because other treatments, such as glasses or contact lenses, are considered to be equally, if not more, effective.

This means you'll usually have to pay for surgery privately.

Prices can vary depending on where you live, the individual clinic, and the type of equipment used during the procedure.

As a rough estimate, you usually have to pay somewhere around £800 to £1,500 for each eye.

Lens implant surgery

Lens implant surgery is a relatively new type of surgery for short-sightedness. It involves implanting an artificial lens into your eye through a small cut in your cornea.

The lenses are specially designed to help focus light more clearly on to the retina.

They can be helpful in improving the vision of people with very severe short-sightedness or those who have difficulty wearing glasses or contact lenses.

There are 2 main types of lens implant:

• phakic implant – where an artificial lens is placed into your eye without removing your natural lens; usually preferred for younger people whose natural reading vision is normal
• artificial replacement – where the natural lens is removed and replaced with an artificial one, similar to cataract surgery

Both types of implant are usually inserted under a local anaesthetic and you'll normally be able to return home the same day. Each eye will usually be treated on separate occasions.

Results

Phakic lens implants may achieve better results than lens replacements in terms of improving vision on a long-term basis. But the technique carries a higher risk of complications, such as cataracts.

Overall, most people will experience a significant improvement in their vision. Around 1 in 4 may have almost completely normal vision ("20/20" vision) afterwards.

A lens replacement may be more suitable for older adults with damage to their eyes or an eye condition other than short-sightedness, such as cataracts or glaucoma.

Also, as both techniques are relatively new, there's little information about whether they're safe or effective in the long term.

Risks and complications

Like all medical procedures, surgery to place artificial lens implants in the eyes carries a risk of complications.

Posterior capsule opacification (PCO) is one of the most common complications of lens implant surgery. This is where part of the artificial lens becomes thickened and cloudy.

PCO usually occurs a few months or years after having surgery. Treatment for PCO can involve having laser surgery to remove the thickened part of the lens.

Other possible complications of lens implant surgery include:

• retinal detachment (where the retina begins to pull away from the blood vessels that supply it with oxygen and nutrients)
• cataracts
• seeing a halo of light around objects at night
• reduced night vision
• glaucoma

You should talk to your doctor or surgeon about each procedure so you're fully aware of any risks involved.

Availability and cost

As with laser surgery, lens implant surgery isn't usually available on the NHS.

Both types of surgery can be quite expensive, with many clinics quoting prices of around £4,000 to £5,000 to treat both eyes.

Can I stop short-sightedness getting worse?

Unfortunately, short-sightedness in children tends to get worse as they grow.

The younger they are when they start becoming short-sighted, generally the faster their vision deteriorates and the more severe it is in adulthood.

Short-sightedness usually stops getting worse at around the age of 20.

There's currently no single treatment available that appears to stop this progression.

But it may be slowed by treatments involving eye drops of a medication called atropine, or special contact lenses.

Research has shown that atropine eye drops can slow the progression of short-sightedness, but it can cause side effects at high strengths (such as difficulty reading and sensitivity to bright light).

Low-strength drops aren't commercially available in the UK.

Orthokeratology and bifocal contact lenses may also slow down short-sight progression in children, but possibly not as much as the eye drops, and they carry small risks.