Lazy eye (amblyopia)
A child with lazy eye, or amblyopia, sees less well out of one eye.
Lazy eye is common, affecting around one in 50 children in the UK.
Usually the other eye makes up for problems with the lazy eye, but treatment is recommended to help prevent long term vision problems.
What causes amblyopia?
Amblyopia usually starts when one eye has much better focus than the other eye. For example, one eye might be very nearsighted or have a lot of astigmatism (an optical defect that causes blurred vision), while the other does not. When the child's brain is confronted with both a blurry image and a clear image, it will begin to ignore the blurry image. If this goes on for months or years, the vision in the eye that sees the blurry image will deteriorate.
Another cause of amblyopia is called strabismus or squint. Strabismus is an ocular misalignment, meaning that one eye turns inward or outward. This prevents the eyes from focusing together on an image and can cause double vision. In order to combat this, the child's brain generally chooses to ignore the image from the deviated eye, causing the vision in that eye to deteriorate. Because one of the eyes is misaligned, some people refer to this as a "lazy eye."
Other children cannot see well in one eye because something blocks light from getting through. This could be due, among other causes, to a cataract or a small amount of blood or other material in the back of the eye.
How is amblyopia diagnosed?
The condition is often not diagnosed until a child has their first eye test. Children are usually given a routine eye examination before they start school as part of the school entry health check. Every young person age 16 or under is entitled to free NHS eye tests.
During the pre-school screening, your child will be checked for a range of common visual impairments by a trained orthoptist (someone who diagnoses and treats problems with vision). This is likely to take the form of a standard eye test (also known as a vision acuity test), where the child is asked to read lines of letters from a chart. Your child may be referred to an ophthalmologist for further investigation if evidence of visual impairment is found.
All children should be screened before they are school age. However, if parents notice any squinting or crossing of the eyes or are concerned about their child's vision, they should be evaluated promptly. Family history of amblyopia is a risk factor for amblyopia. Parents cannot tell just by looking at their child if they have amblyopia. Early diagnosis and treatment are the keys to the best visual outcome.