Astigmatism is usually diagnosed after a routine eye test.
Regular eye tests
Most people who have astigmatism are born with the condition, so it's important your children have regular eye tests.
Children may not realise there's anything wrong with their vision. If their vision isn't regularly tested, conditions like astigmatism could remain undiagnosed for many years, which can cause a lazy eye.
If a child has uncorrected astigmatism, they may have difficulty reading and concentrating at school.
When to get tested
Your baby will have their eyes examined at birth or shortly afterwards (within 72 hours) to check for any obvious defects.
They'll have a second eye examination when they're between 6 and 8 weeks old, which will usually be carried out by your GP.
Your child's vision may also be checked when they start school at around five years of age, but this varies depending on where you live.
Read more about children's routine eye tests.
If your child has suspected vision problems, they may be referred to an orthoptist. An orthoptist specialises in problems relating to eye movements and vision development. They usually work in local health clinics or hospital eye clinics.
Eyesight problems may also be investigated by an ophthalmologist (a medical doctor who specialises in diagnosing and treating eye conditions). They mainly work in hospitals and hospital eye departments.
You may also see an optometrist. Optometrists examine eyes, test sight, and prescribe glasses and contact lenses. They're trained to recognise eye conditions and sight defects.
If your child's vision has been checked and is normal, they should continue to have regular eye checks about once every year.
Adults should have an eye test at least once every two years, unless advised otherwise by their optometrist.
Read more about children's eyes and NHS eye care services.
Testing for astigmatism
A number of tests can be used if astigmatism is suspected. The two most common tests are the visual acuity test and the keratometer test.
Visual acuity test
A visual acuity test can be used to assess your or your child's ability to focus on objects at different distances. It usually involves reading letters on a chart called a Snellen chart. The letters become progressively smaller on each line of the chart.
A device called a keratometer can measure the degree of corneal astigmatism. It measures how light is being focused by the cornea and can detect irregularities in the curve of the cornea.