Myopia (short-sightedness): symptoms, causes and treatment

Short-sightedness is a refractive error, which simply means the eye does not bend light to a precise focus on the retina at the back of the eye. In most people with myopia the eyeball has grown slightly too long, so the image of a faraway object comes to a point in front of the retina. Close objects, which need more focusing power, are often still clear without any help. There are different degrees of short-sightedness, from a mild prescription that only matters for driving or the cinema to a strong one that leaves everything beyond arm's length blurred.

Because the blur affects distance rather than near vision, children often do not realise anything is wrong. They assume everyone sees the classroom board the way they do. That is why the signs tend to be noticed indirectly, by parents and teachers rather than by the child.

• Difficulty reading words from a distance, such as the whiteboard at school.

• Sitting very close to the television or computer, or holding a phone or tablet close to the face.

• Narrowing the eyelids (squinting) to see distant things more clearly, or moving closer to them.

• Headaches and frequent eye rubbing.

The exact causes are not fully understood, which is why it is hard to predict how short-sighted a child will eventually become. The College of Optometrists lists several things that make childhood myopia more likely: having one or both parents with myopia, being of east-Asian ethnic origin, spending limited time outdoors and doing a lot of prolonged near-vision activity. The NHS also notes that it often runs in families.

Age of onset matters. The College says that becoming myopic before the age of nine may increase the chance of developing a high level of myopia, because there are more years in which the eye can keep lengthening. Screen use is a common worry for parents. The College describes the evidence that long periods of reading and screen use affect myopia development as not strong, and says there is no evidence that using a screen damages the eyes. The practical concern is more that time on screens can displace time outdoors.

The NHS advises going to an optician if you or your child has signs of short-sightedness, or if you have not had an eye test for two years. The test is carried out by an optometrist. You will be asked to look at a light or read letters on a chart while different lenses are placed in front of your eyes, which lets the optometrist find the lens strength that gives the clearest vision. Eye drops may be used so the back of the eye can be examined more clearly. If you need glasses you are given a prescription that can be taken to any optician.

NHS-funded sight tests are free for some groups, including children under 16, 16 to 18-year-olds in full-time education, people aged 60 or over, and people with diabetes or glaucoma, as well as people on certain benefits. Some people are also entitled to an NHS optical voucher towards glasses or contact lenses. Eligibility rules change, so the optician or the NHS website is the place to confirm them.

Myopia is usually easy to correct. Glasses suit both children and adults. Contact lenses are suitable for adults and for some children, and the optician advises on which is better for the individual. Both help the eye focus correctly; neither changes how quickly a child's myopia progresses, according to the College of Optometrists.

Some adults choose surgery. The NHS describes two types: laser surgery that reshapes the front of the eye, and lens surgery that replaces the eye's own lenses with artificial ones. It says this surgery is not available on the NHS and can be expensive. The procedures, risks and who is suitable are covered in the linked laser eye surgery guide. The NHS notes that short-sightedness can keep getting worse until the eye has stopped growing, usually at around 20 years of age, which is worth bearing in mind when thinking about timing.

Parents often ask whether anything can slow the change in their child's prescription. The College of Optometrists says that spending more time outdoors can help prevent or delay myopia developing, particularly for children at higher risk, and that it may also slow how quickly it increases, although it states that more research is needed to be sure. It suggests balancing reading and screen time with outdoor time and following the 20-20-20 rule: every 20 minutes, look at something at least 20 feet away for about 20 seconds.

Treatments that may slow progression in childhood are called myopia management or myopia control. The College lists three used in the UK: myopia management contact lenses, myopia management spectacles and orthokeratology lenses, which are rigid gas-permeable lenses worn overnight. It says they have similar results to one another. It also says the long-term effect on later sight-threatening conditions is not yet known, and that there is not enough evidence to say whether the long-term benefits outweigh the costs, so some families reasonably stay with ordinary glasses.

None of these is funded by the NHS anywhere in the UK, which means families pay for them privately, usually through an optometrist. The NHS says more research is needed before they could be offered on the NHS.

For most people myopia is only a nuisance corrected by lenses. The NHS notes that young children with uncorrected short-sightedness may be more likely to develop a squint or a lazy eye, which is one reason tests for children matter.

In adults, severe myopia is linked with other eye conditions. The NHS lists glaucoma, a detached retina (which needs urgent treatment to prevent sight loss), cataracts and macular degeneration. The College of Optometrists describes the risk of retinal detachment, glaucoma and myopic retinal degeneration as slightly greater with a high level of myopia, and stresses regular sight tests so any change is picked up early.

• Because a detached retina needs urgent treatment, any sudden change such as new flashes, a rush of floaters or a shadow across vision should be assessed urgently; use NHS 111 or A&E if an optometrist cannot see you the same day.

Most myopia is managed entirely in the community: an optometrist tests the eyes, issues a prescription and reviews it, with the NHS advising a test at least every two years. A GP or hospital eye clinic is involved only if the optometrist finds a related condition or something unexpected. Private care is mainly relevant for options the NHS does not provide: myopia control lenses, orthokeratology, laser surgery and lens surgery. These are normally arranged directly with an optometrist or eye surgeon, and prices vary widely between providers, so ask for a written breakdown of the assessment, the treatment and the aftercare that follows.