A lazy eye (amblyopia) is a childhood condition where the vision in one eye doesn't develop properly. 

This usually means that the child can see less clearly out of the affected eye and relies more on the "good" eye.

An estimated 1 in 30 to 1 in 50 children will develop a lazy eye. The condition is usually diagnosed around the age of four.

Lazy eye can sometimes affect both eyes, although this is rare.

How do I know if my child has a lazy eye?

A lazy eye doesn't usually cause symptoms. Younger children are often unaware that there's anything wrong with their vision and, if they are, they're usually unable to explain what's wrong.

Older children may complain that they can't see as well through one eye and have problems with reading, writing and drawing.

In some cases, you may notice that one eye looks different from the other.

However, this is usually a sign of another condition that could lead to a lazy eye, such as:

  • a squint – where the weaker eye looks inwards, outwards, upwards or downwards, while the other eye looks forwards
  • refractive errors – where a person is either short-sighted (myopia) or long-sighted (hyperopia)
  • childhood cataracts – cloudy patches that develop in the lens, which is located behind the clear layer of tissue at the front of the eye (cornea) 

One way to check your child's eyes is to cover each eye with your hand, one at a time. They might object to covering the good eye, but they might not mind if you cover the lazy eye.

If they try to push your hand away from one eye but not the other, it may be a sign they can see better out of one eye.

When to seek medical advice

Lazy eye is often diagnosed during routine eye tests before parents realise there's a problem. 

Children should have their eyes tested once they're old enough to attend a sight test, which is usually after they are 3.5 years old.

It's difficult to treat lazy eye after the age of 4.5, so it's a good idea for children to have an eye test between the ages of 3.5 and 4.5.

However, visit your GP if you have any concerns about your child's eyesight. If necessary, they can refer your child to an eye specialist (ophthalmologist) for further testing.

Read more about diagnosing a lazy eye.

What causes a lazy eye?

The eyes work like a camera. Light passes through the lens of each eye and reaches a light-sensitive layer of tissue at the back of the eye called the retina.

The retina translates the image into nerve signals that are sent to the brain. The brain combines the signals from each eye into a three-dimensional image.

A lazy eye occurs when the brain connections responsible for vision aren't made properly.

This can be the result of:

  • a reduction in the amount of light entering the eye
  • a lack of focus in the eye
  • confusion between the eyes – where the two images aren't the same (such as a squint)

Left untreated, this can lead to the eye's central vision never reaching normal levels.

Read more about the causes of a lazy eye.

Treating a lazy eye

In most cases it is possible to treat a lazy eye, usually in two stages.

The underlying problem is first corrected using glasses to correct the focus of the eye, which often helps to correct a squint as well.

The child is then encouraged to use the affected eye again. This can be done using an eye patch to cover the stronger eye, or eye drops to temporarily impair the vision in the stronger eye.

Treatment is often effective, but it's a gradual process that takes many months to work.

Read more about treating a lazy eye.

Page last reviewed: 16/06/2016

Next review due: 31/05/2019