The short answerA lazy eye (amblyopia) is reduced vision, usually in one eye, that develops because in early childhood the brain relied on the other eye, so vision from the weaker eye did not develop properly. The main causes are a squint, a big difference in glasses prescription between the eyes, or something blocking vision, such as a congenital cataract or a drooping eyelid. Treatment starts with glasses, then patching the stronger eye or special eye drops under an ophthalmologist, and the earlier it starts, the better the result.
What is a lazy eye?
With a lazy eye, the eye itself can look completely normal. The problem lies in how vision develops between the eye and the brain. In the first years of life the brain learns to see, and if one eye's image is blurred or misaligned for a long time, the brain ignores it and relies on the other eye. The result is that the weaker eye cannot reach 6/6 even with the right glasses. Both eyes can be affected if both have a high uncorrected prescription.
Causes of a lazy eye
- Squint: when one eye turns, the brain ignores its image to avoid double vision. Read about squint in children.
- Different prescriptions in each eye: one eye needs strong glasses and the other does not. This cause is hidden because both eyes look normal, and the child does not complain because they see well with the stronger eye.
- Something blocking vision: anything that stops a clear image reaching the retina, such as a congenital cataract, a drooping eyelid covering the pupil, or a cloudy cornea. This type is the most urgent and the cause needs treating early.
- A high prescription in both eyes: strong short-sightedness, long-sightedness or astigmatism left uncorrected during the growing years.
Why timing matters
Vision develops fastest in the first years of life, and this is when the brain responds best to treatment. The best results come from treating children while they are young, and the response gradually falls with age. That does not mean it is too late for older children: many of them, and some teenagers, still improve with treatment, though usually less. A lazy eye does not get better on its own, and if left untreated the reduced vision can be permanent.
Signs parents may notice
- An eye that turns in or out, all the time or now and then.
- Tilting the head or closing one eye to look at things.
- The child objects or cries when one particular eye is covered, but not the other.
- Bumping into things on one side, or sitting very close to screens or books.
- A drooping eyelid covering part of the pupil.
- A white reflection in the pupil in flash photos, or a different coloured reflection in each eye. This needs an urgent exam.
Many children with a lazy eye show no signs at all, because the stronger eye makes up for it. An eye test is the only reliable way to find it.
Each eye must be tested on its own
If a child looks with both eyes, the result will seem normal because the stronger eye reads the chart. One eye must be covered while the other is tested, then the other way round, which a quick school check can miss. Every child should have a vision check before starting school, and straight away at any age if any of the signs above appear or there is a family history of lazy eye, squint or strong glasses in childhood. Measuring a child's prescription usually needs dilating drops, because their strong focusing muscles can hide long-sightedness.
Treatment
Glasses first
If the cause is a prescription that needs correcting, glasses come first and the child wears them all day. Glasses alone clearly improve vision in many children over weeks to months, after which the doctor decides whether more treatment is needed.
Patching the stronger eye
An adhesive patch goes over the stronger eye for a number of hours a day set by the doctor, so the brain has to use the weaker eye. A patch stuck on the skin usually works better than covering the glasses lens, because children can peek around it. Close-up activities such as drawing, colouring and games help while the patch is on.
Atropine drops
An alternative to patching in some cases: drops in the stronger eye temporarily blur its near vision, so the child relies on the weaker eye. They can cause light sensitivity and are only used as prescribed, at the dose the doctor sets.
Treating the cause
Where something blocks vision, such as a congenital cataract or a severely drooping eyelid, the cause must be treated first so a clear image reaches the eye. The child then continues lazy eye treatment.
Do not patch your child's eye or use drops without an ophthalmologist's supervision. Too much patching can weaken the stronger eye. Treatment lasts months with regular visits, and a lazy eye can come back after treatment stops, so follow-up continues for a while.
Frequently asked questions
Up to what age can a lazy eye be treated?
Results are better the younger the child. But many older children and some teenagers still improve with treatment, though usually less. Do not wait, and let the doctor advise on what is possible for your child.
Will a lazy eye go away on its own?
No. A lazy eye does not improve by itself as the child grows, and waiting lowers the chance of improvement. It needs diagnosis, treatment and follow-up.
How many hours a day should a child wear an eye patch?
It depends on how weak the eye is, the child's age and how they respond. It may be two hours a day in moderate cases and more in severe ones. The doctor sets the time and adjusts it at each visit.
Will glasses make my child's eyes weaker?
No. The right glasses do not weaken the eyes. They give the brain the clear image it needs for vision to develop, and they are the basis of lazy eye treatment.