Lazy eye (amblyopia): symptoms, treatment and how it is found

The NHS says how a lazy eye is treated depends on what is causing it, and that the aim of treatment is to improve vision in the weaker eye. The options it lists are glasses to correct vision, an eye patch worn over the stronger eye for a few hours a day for several months, and eye drops that temporarily blur vision in the stronger eye. The patch is usually worn together with glasses.

The idea behind patches and drops is that covering or blurring the stronger eye encourages the weaker eye to be used. The routine can feel like a lot of effort for a child whose good eye sees perfectly well, so it helps to ask the eye care team to explain the plan to your child as well as to you.

The NHS says treatment should ideally start before the age of 7, when vision is still developing. It does not say that treatment is pointless afterwards, only that this is the point at which it works best, so a child whose problem is found late should still be seen and assessed rather than written off.

• Glasses or contact lenses to correct the vision in each eye.

• An eye patch over the stronger eye, usually for a few hours a day and for several months.

• Eye drops that temporarily blur the vision in the stronger eye.

• Surgery when the cause is a cataract, a drooping eyelid or a squint.

The NHS says a lazy eye does not always cause symptoms, which is why it is so often found by chance on an eye test. When there are signs, the NHS lists the following. Not every child has all of them, and several of them are also common in children who see perfectly well, so they are a reason to book an eye test rather than a diagnosis.

• Shutting 1 eye or squinting when looking at things.

• Eyes pointing in different directions (a squint).

• Not being able to follow an object or person with the eyes.

• Tilting the head when looking at something.

• Tired eyes and rubbing the eyes a lot.

• Headaches.

• Difficulty catching or throwing.

• Tripping or falling over a lot.

• Blinking a lot.

Lazy eye is mainly a childhood condition because it is about how vision develops. The NHS says many children do not notice anything wrong with their vision. That matters, because a child who has always seen less well with one eye has nothing to compare it with and is unlikely to complain.

The NHS suggests a simple home check for a younger child: cover each eye with your hand, one at a time. They may complain when you cover the good eye. Older children may say they cannot see as well with one eye. A check at home does not replace an eye test, but it can prompt you to book one.

The NHS eye-test guidance describes when children are checked. The newborn physical examination looks at the eyes within 72 hours of birth, with a follow-up at 6 to 8 weeks. Around 4 or 5 years old, vision screening checks for reduced vision in one or both eyes soon after starting school. The NHS says this is usually carried out in school but does not happen in all areas, so if your child has not had one, take them to a local optician. Children can have an eye test at any age and do not need to be able to read or speak.

In a lazy eye, the eye itself is usually healthy but the vision in it does not develop properly. The NHS describes it as vision in 1 eye that does not develop properly, and rarely both eyes. The word "lazy" can be misleading. The eye is not idle and the child is not at fault. It is a problem of vision development that is usually fixable when it is found early.

A lazy eye is related to a squint but is not the same thing. A squint (strabismus) is when the eyes point in different directions. The NHS squint page says that if a child has a lazy eye as a result of their squint it may need to be treated first, and that treating a lazy eye usually involves a patch over the unaffected eye.

The NHS says how a lazy eye is treated depends on what is causing it, and it names several causes along the way. The NHS squint page explains that a squint can lead to a lazy eye, where the brain starts to ignore signals coming from the affected eye so the child does not develop normal eyesight. The lazy eye page names cataracts and a drooping eyelid as causes that may need surgery.

The NHS squint page also explains that in children a squint is often caused by the eye attempting to overcome a vision problem such as short-sightedness, long-sightedness or astigmatism. Put together, the common routes to a lazy eye are a squint, a vision problem that is different between the eyes or that has not been corrected, or something physically blocking vision such as a cataract or a drooping eyelid. An eye care professional works out which applies to a particular child.

The NHS says an eye test specialist called an optometrist will usually do an eye test to check for a lazy eye. You or your child are asked to look at lights or read letters while different lenses are placed in front of the eyes. To check the health of the eyes, eye drops may be given so the optometrist can see the back of the eye more clearly. If glasses are needed, you are given a prescription that you can take to any optician.

For babies and young children who cannot read letters, the NHS describes simpler methods: checking whether a baby pays attention to visual objects, using pictures or symbols instead of letters, and testing eye movement by drawing a child's attention to an object moved to different positions. The NHS also describes a red reflex test at newborn checks, in which a white reflection instead of a red one could be a sign of an eye problem.

A lazy eye is not an emergency, but it should not be left. The NHS says to go to an optician if you are worried about your or your child's vision or if you have not had an eye test for 2 years. The NHS squint page adds that you should get advice if your child has a squint all the time, or has a squint that comes and goes and is older than 3 months, as in babies younger than this a squint that comes and goes is common and not usually a cause for concern.

The same page says a squint can sometimes be a symptom of a rare type of childhood eye cancer called retinoblastoma, so a GP should see a child with a squint to rule it out. The NHS newborn eye check also treats a white reflection in place of the usual red one as a possible sign of an eye problem. A white-looking pupil or a new squint should be looked at promptly by a GP or optician.

• A squint that is there all the time.

• A squint that comes and goes in a child older than 3 months.

• A white reflection in the pupil instead of the usual red reflection.

• Any worry about your child's vision at any stage.

• A new squint or double vision developing later in life.

The NHS says treatment should ideally start before the age of 7. The NHS lazy eye page does not set out a separate treatment route for adults with a long-standing lazy eye, so the sensible step is to have an eye test, tell the optometrist about any history of lazy eye or squint, and ask what the results mean for you. NHS eye tests are free for some people, including those who have diabetes or glaucoma, and those on some benefits including Universal Credit.

If a squint is present, the NHS squint page says surgery can help improve the alignment of the eyes even if a squint has been left untreated for a long time, but that any vision problems may be permanent if they are not treated at a young age.

The NHS lazy eye page says you may need to have surgery if you have a squint. It says the operation straightens the eyes and allows them to work together better, but does not improve vision. That is why a lazy eye and a squint are often managed together, with treatment of the weaker eye and surgery for the alignment as separate steps.

The NHS squint surgery page says the operation involves moving the muscles that control eye movement so the eyes line up better. It is done under general anaesthetic and usually takes less than an hour, and you or your child can usually go home the same day. It lists risks including further surgery being needed to fully correct the squint, which it says is quite common if the squint is severe, and permanent double vision. Loss of vision is described as very rare.

In the NHS pathway, a lazy eye is usually picked up through the child health checks and school vision screening described above, or at an optician. A GP, health visitor or local optician service can refer a child with a squint to an eye specialist for tests and treatment if necessary. Glasses are prescribed after an eye test and can be used at any optician.

The NHS says some people are entitled to a voucher to help towards the cost of glasses or contact lenses, including children aged under 16, or 16 to 18 and in full-time education, people with diabetes or glaucoma, and people on some benefits. Without a voucher you pay for glasses or contact lenses. Some families choose to see an optometrist or eye specialist privately, for example for speed or choice of appointment. The tests and treatment options described on this page are the same in either route, and the result should be shared with the GP.