At a glance
- In lazy eye (amblyopia), the child’s vision doesn’t develop properly.
- This problem can occur if a child has a squint or worse eyesight in one eye.
- The brain then “ignores” the weaker (lazy) eye.
- Special vision tests can be done to diagnose lazy eye, even in young children.
- Glasses, eye patches or eye drops can help to improve vision.
Normally, our brain processes the images sent by both eyes equally. This is needed for the best possible vision.
In some children, though, one eye is favored by the brain because it provides a sharper image. The brain then ignores the images from the other eye. As a result, the child's vision doesn’t develop properly because the information from the weaker eye is no longer used. This is known as amblyopia, or “lazy eye.”
If your child has a squint or trouble recognizing things, it could be a sign of lazy eye. They may, for instance, have to hold toys or other objects very close to their eye to see them properly, or always turn their head to one side when looking at things.
Amblyopia develops when the two eyes keep sending such different images to the brain that the brain can’t merge them into one. The most common cause of this is a squint (strabismus). If a child has a squint, one eye will look straight ahead while the other looks up, down or to the side, so it is taking in a completely different image. In an effort to avoid seeing double, the brain often blocks out the images from the eye that doesn’t see as well, and relies on just one eye.
About 60 to 70% of children who have a squint have a lazy eye because of this, compared to only 2% of children who don’t have a squint.
Refractive errors are another common cause of amblyopia. They make the image that appears on the retina of the eye blurry. There are three different kinds of refractive error:
- Nearsightedness (shortsightedness or myopia): The eye can only focus clearly on objects that are close by. When looking into the distance, though, the lens can’t bend the incoming light in a way that results in a clear image on the retina. This might happen if, for instance, the eyeball is a little too long.
- Farsightedness (hyperopia): The eye can only focus clearly on objects that are far away. When looking at things close-up (e.g. when reading) the lens can’t bend the incoming light enough, for instance because the eyeball is too short.
- Astigmatism (not shown in the illustration): Everything appears blurry because the lens or the cornea is deformed.
Refractive errors are more likely to lead to a lazy eye if each eye is affected in different ways:
- one eye is farsighted or nearsighted and the other one is normal.
- one eye is farsighted and the other is nearsighted.
Lazy eye is only rarely caused by another eye disorder. Eye disorders that can cause lazy eye include a cloudy lens at birth (congenital cataracts), a droopy eyelid (called ptosis) or a missing eye lens (aphakia) at birth.
Lazy eye is a common vision problem in children and young adults. It is estimated that about 3% of children and young people in Europe are affected overall, and up to 6% of preschool children.
Lazy eye is equally common in boys and girls. It usually develops before the age of 7.
There are several tests that eye doctors can do to find out whether a child has amblyopia:
Eye charts: Doctors can use eye charts to find out how well a child can see. The child is asked to read things like numbers or letters from an eye chart or screen.
Eye charts for younger children may have simple symbols on them – like a circle, a house or an apple – and the child is asked to say what they can see. Or there might be symbols that look like the letter C (a broken ring) or E.
Different types of eye charts
The symbols are arranged in rows on the charts and face in different directions. Then the child is asked to say where the “gap” in the C-shaped ring is, for example. Or they are given a kind of E-shaped plastic fork and are asked to hold it in the same direction as the symbol they are looking at.
Retinoscopy: Toddlers and babies can have an examination using an instrument known as a retinoscope. Here the child doesn’t have to recognize anything or say what they can see. Instead, the doctor shines a light into the child’s eye and observes how the light reflects off the retina at the back of the eye. By holding various corrective lenses in front of the light beam, the doctor can find out exactly how farsighted or nearsighted the child is in that eye.
Covering one eye: A slight squint isn’t always visible to the naked eye. To tell whether a child has a squint, the position of their eyes can be measured – for instance, with a test in which the eyes are covered one at a time. The doctor then checks whether the other eye moves.
These tests are generally safe. Depending on the equipment used, eye drops are typically given to dilate (open) the pupils before examining the eyes with a retinoscope. The eye drops occasionally cause skin irritations or burning in the eyes.
Specialists believe that eyesight mainly develops in the first five years of life. They think that lazy eye should be detected and treated as early as possible in order to avoid lifelong vision problems, as well as problems at school and in the child's social development.
For this reason, an extra screening test was introduced in Germany for all preschool children who have statutory health insurance. This test is called “U7a” in the German health care system, and its main aim is to detect vision problems. It is offered in addition to the existing screening examinations for children in Germany (the so-called “U-Untersuchungen”), and is aimed at toddlers who are nearly three years old (between 33 and 35 months old).
Lazy eye can’t be fixed instantly by putting on glasses that correct the problem. But there are a number of different ways to improve vision in the weaker eye – for instance with glasses, an eye patch on the stronger eye, or with eye drops. Treatment might only be needed for a few weeks.
Although it can sometimes take quite a long time to get good results, lazy eye can be treated successfully in most children.
If another eye problem (e.g. a droopy eyelid) is causing the lazy eye, that problem is treated first.
When people are ill or need medical advice, they usually go to see their family doctor or pediatrician first. Read about how to find the right doctor, how to prepare for the appointment and what to remember.
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