Astigmatism

Astigmatism

In many cases, the symptoms of astigmatism are so mild that no treatment is required

Astigmatism is a minor eye condition. The main symptom of astigmatism is blurred vision.

Astigmatism occurs when the cornea (the front of the eye) is not a perfectly curved shape. The cornea should be shaped like a football (soccerball) but in cases of astigmatism, it has an irregular curve (like a rugby ball), with one half flatter or steeper than the other. This means the light rays that come into the eye do not focus properly on the retina at the back of the eye, creating a blurred image.

Refractive errors

Astigmatism belongs to a group of related eye conditions known as refractive errors. Other common refractive errors include:

  • Short-sightedness (myopia).

  • Long-sightedness (hypermetropia).

How common is astigmatism?

Astigmatism is a very common eye condition and is usually present at birth (congenital). However, it can sometimes develop following an injury to the eye, or as a side effect of an eye operation.

Outlook

Symptoms of blurred vision do not usually change over time (they neither get better or worse).

In many cases, the symptoms of astigmatism are so mild that no treatment is required. In cases where vision is significantly affected by astigmatism, it can be corrected with glasses or contact lenses.

Laser treatment is also being more commonly used to treat astigmatism.

To understand the causes of astigmatism, it is useful to understand how the eye works.

How the eye works

The eye works in a similar way to a conventional camera and is made up of three parts:

  • The cornea and lens: situated at the front of the eye they act like a camera lens helping to focus the light coming into the eye.
  • The retina (at the back of the eye): is like the film in a camera. It is a light-sensitive layer of tissue that can capture and store an image produced from the incoming light.
  • The optic nerve: transmits the image that is stored on the retina to the brain.

Astigmatism usually occurs as a result of problems with the cornea.

The cornea

The cornea is a transparent layer of tissue that covers the front of the eye. It helps to protect the eye from damage and infection. The cornea and lens are also responsible for focusing incoming light onto the retina to create a clear image.

To work properly, the cornea needs to be perfectly curved – like the top half of a football. However, in cases of astigmatism, the curve of the cornea is imperfect, with one half either being steeper or flatter than the other part.

When light hits an imperfectly curved cornea, the retina does not receive a perfectly sharp image of light. Instead, the light is slightly ‘smeared’, resulting in blurred vision.

The reasons why some people are born with an imperfectly curved cornea are unknown. However, there is some limited evidence that the condition can run in families.

Being born prematurely, and/or with a low birth weight, may also increase the risk of a child developing astigmatism. This may be because the eye does not have time to fully develop in the womb.

Injuries to the cornea can also result in astigmatism, as can damage to the cornea caused by eye surgery.

Regular eye tests

As most people who have astigmatism are born with the condition it is very important that your children receive regular eye tests.

If your child has been born with astigmatism they are unlikely to realise that there is anything wrong with their vision, so if their vision is not regularly tested, conditions like astigmatism could remain undiagnosed for many years. Undiagnosed astigmatism can affect a child’s learning and development because they may have problems reading and concentrating at school.

Your child will receive an eye test shortly after they are born, and a follow-up test six weeks later.

A comprehensive eye test is also recommended once your child reaches the age of four. By this age, if they have an eye condition, it should be able to be diagnosed through testing.

Children should then have an annual eye test until they are 16 years of age.

Adults over the age of 16 usually only require an eye test every two years, unless advised otherwise by their optician.

Testing for astigmatism

There are a number of tests that can be used to diagnosis astigmatism. One test, known as a visual acuity test, can be used to assess your, or your child’s, ability to focus on objects at different distances.

The visual acuity test usually involves reading letters on a chart, where the letters become progressively smaller on each line.

Another test uses a piece of equipment called an astigmatic dial. This is a chart, or panel, that shows a series of lines making up a semi-circle. People with astigmatism will usually see some lines more clearly than others.

A device called a keratometer can be used to measure the degree of astigmatism. It can measure how light is being focused by the cornea and detect any imperfections in the curve of the cornea.

The symptoms of astigmatism include:

Blurred vision.
Sensitivity to light (photophobia),
Headaches
Eye strain and fatigue (particularly after carrying out tasks that require focusing on something for a long period of time, such as reading or using a computer).