Astigmatism assessment

Astigmatism is a common eye condition that causes blurry or distorted vision.

At St Joseph’s Hospital, our eye consultants (ophthalmologists) can provide you with a comprehensive eye examination to test for astigmatism, and then talk you through the different treatment options available to you.

What is astigmatism?

The normal shape of the front surface of the human eye is smooth and round.

Light enters the eye through the cornea (the clear surface covering the front of the eye) and passes through the pupil. Upon reaching the lens of the eye, the light is focused onto a particular part of the nerve layer lining the back of the eye, known as the retina.

The retina converts the light into an electrical signal and then sends it via the optical nerve to the brain for visual processing.

When the front of the eye is shaped normally, the cornea and lens focus light correctly onto the retina, leading to a sharp, clear image being seen.

While a regularly-shaped eye resembles the shape of a football, a person with astigmatism will have the front surface of the eye shaped more like a rugby ball, with an irregularity in the cornea.

This change in the shape of the cornea alters the way that light enters the eye, and the way it is then focused onto the retina. Instead of light being focused on a particular point of the retina, it is focussed on a number of different areas.

This causes a less focussed, blurry image to be seen.

If left uncorrected, astigmatism can cause:

  • blurry or distorted vision,
  • headaches,
  • eye strain.

People are usually born with astigmatism, although it can also develop later in life. People with astigmatism are more likely to be short- or long-sighted.

You are more likely to develop astigmatism if you:

  • have a family history of it,
  • are extremely short-sighted (myopic),
  • are extremely long sighted (hyperopic),
  • have previously had eye surgery,
  • have had an eye injury.

A specialist eye doctor (ophthalmologist) can test for astigmatism as part of a comprehensive eye examination.

As astigmatism is caused by a defect in the curvature of the cornea, they will test how your eye is currently focussing light.

This can be done using a number of tests, such as:

Visual acuity tests: The ‘classic’ eye test, you will be asked to read a series of letters of varying heights on a chart a specific distance from you.

This helps to assess how clearly you are able to see objects A normal visual acuity is referred to as 20/20 vision.  


A retinoscope is a diagnostic eye instrument that shines a bright light into your eye.

Holding a number of different lenses between your eye and the light source, the ophthalmologist is able to assess the reflection of light off your retina.

This test is quick and easy to carry out and can give a good indication of whether astigmatism is present.


A keratometer is a device used to measure the curvature of your cornea.

This can be a helpful way to assess whether an excess curvature of the cornea is the cause of any astigmatism.

Corneal topography

A non-invasive diagnostic imaging technique that maps the curve of your cornea. This shows whether there are any imperfections in the cornea that are causing astigmatism. 

Should your vision be affected by astigmatism, there are different ways it can be corrected:

Glasses: A prescription lens can often compensate for the effect of your astigmatism.

Contact Lenses: some people prefer to wear contact lenses instead of glasses. For example, people who play contact sports tend to prefer contact lenses.

Laser eye treatment: specialised laser technology can be used to correct and reshape an imperfection in the cornea.

Once you have had your eye examination, the ophthalmologist will be able to give you the results of the tests.

Should you have astigmatism in either eye, they will be able to talk you through your treatment options and help you decide the best way forward.

If you have any queries or concerns, you will be able to ask them for their expert advice.

We know that experiencing a change in your vision can be unsettling. Should you be experiencing any changes in your sight, such as blurriness or eye strain, contact us to book your eye examination.

The consultant-led ophthalmology team at St Joseph’s Hospital is at the forefront of ophthalmic care in the UK, and we have world leading technology to help with your diagnosis and treatment.

Our experienced consultants can provide you with a thorough eye examination to determine whether you have astigmatism, and then help you choose the optimal way of compensating for it while maintaining good eye health.

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