A lazy eye ideally needs to be diagnosed and treated as early as possible, preferably before a child is 6 years of age.
However, it can often be difficult to know whether a child has a lazy eye as they might not realise anything is wrong with their vision.
This means a lazy eye may not be diagnosed until a child has their first eye test.
If an eye specialist suspects a lazy eye, they'll also test for other conditions, such as a squint.
Visit your GP or tell your health visitor if you have any concerns about your child's eyesight at any stage.
You can also take your child to a high-street optician, where they'll be seen by an optometrist (a specially trained optician).
Your baby's eyes will be examined within 72 hours of birth. This simple examination is used to check for obvious physical problems, such as a cataract.
Your baby will have a second eye examination when they're between 6 and 8 weeks old.
A child's vision should develop in the following way over the first year of life:
Shortly before or after having a baby, all new parents are given a Personal Child Health Record (red book), which highlights developmental milestones for vision.
When your child is around 1 or 2 years old, you may be asked whether you have any concerns about their eyesight during a review of their health and development.
If necessary, specific eye tests that check for vision problems can be arranged.
Your child's vision may also be tested when they start school, at around 4 or 5 years of age. This will be organised by your local council.
Read more about routine eye tests for children.