Astigmatism

What is astigmatism?

Astigmatism is a type of refractive error where the front surface of the eye (the cornea) or the lens inside the eye has an irregular curvature which causes the vision to be distorted and blurred.

For example, instead of having a round, spherical curvature like a basketball, the cornea may be elongated like a rugby ball. Light rays entering an astigmatic eye are bent unevenly. As a result, these rays do not focus at a single point on the retina, causing some parts of the image to be more out of focus than others.

There are a number of different types of astigmatism. These include:

  • simple;
  • compound;
  • mixed;
  • regular;
  • irregular;
  • corneal; and
  • lenticular.

Causes

Astigmatism often occurs with near-sightedness (myopia) and far-sightedness (hypermetropia). The exact cause remains unknown; however, some common types of astigmatism seem to run in families and may be inherited. It is thought that most people have some form of astigmatism as it is rare to find perfectly shaped curves in the cornea and lens, but the defect is rarely serious. Keratoconus is a condition in which the cornea is highly astigmatic and may cause severely distorted vision.

Symptoms

Blurred or distorted vision, eye strain and headaches are possible symptoms of astigmatism.

There are different amounts of blur in different directions.

What your doctor can do for you

  • Perform an eye examination to determine whether you have astigmatism.
  • Refer you to an ophthalmologist or optometrist for correction of the astigmatism with prescription glasses or contact lenses.
  • Refer you to an ophthalmologist (eye specialist) for laser eye surgery, lens surgery or corneal surgery, which can help correct certain types of astigmatism.
Last Reviewed: 14 October 2015
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References

1. National Eye Institute. Facts about astigmatism. https://nei.nih.gov/health/astigmatism (accessed Oct 2015).
2. Mayo Clinic. Astigmatism. Jan 2014. http://www.mayoclinic.org/diseases-conditions/astigmatism/basics/definition/con-20022003 (accessed Sept 2015).
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