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Astigmatism

A disorder of the vision, usually due to a misshapen cornea, such that light does not focus correctly on the retina causing a blurred image.

PubMed Health Glossary
(Source: Wiktionary)

About Astigmatism

Astigmatism is a common type of refractive error. It is a condition in which the eye does not focus light evenly onto the retina, the light-sensitive tissue at the back of the eye.

What is refraction?

Refraction is the bending of light as it passes through one object to another. Vision occurs when light rays are bent (refracted) as they pass through the cornea and the lens. The light is then focused on the retina. The retina converts the light-rays into messages that are sent through the optic nerve to the brain. The brain interprets these messages into the images we see.

How does astigmatism occur?

Astigmatism occurs when light is bent differently depending on where it strikes the cornea and passes through the eyeball. The cornea of a normal eye is curved like a basketball, with the same degree of roundness in all areas. An eye with astigmatism has a cornea that is curved more like a football, with some areas that are steeper or more rounded than others. This can cause images to appear blurry and stretched out.

More about Astigmatism NIH - National Eye Institute

What works? Research summarized

Evidence reviews

Iris-registration in wavefront-guided LASIK versus conventional LASIK for correction of myopia and myopic astigmatism: a meta-analysis

Bibliographic details: Li Y, Cheng SM, Zhou X, Xu L.  Iris-registration in wavefront-guided LASIK versus conventional LASIK for correction of myopia and myopic astigmatism: a meta-analysis. Chinese Journal of Evidence-Based Medicine 2013; 13(3): 358-364 Available from: http://www.cjebm.org.cn/en/oa/DArticle.aspx?type=view&id=20130319

Excimer laser versus phakic intraocular lenses for the correction of moderate to high short‐sightedness

Myopia is a condition in which the focusing power (refraction) of the eye is greater than that required for clear vision of distant objects. Myopia is a common cause of visual disability throughout the world. The World Health Organization (WHO) has grouped myopia and uncorrected refractive error among the leading causes of blindness and vision impairment in the world. The overall power of the lens that would be needed to correct the myopia is expressed in diopters (D) of a sphere. Most people have some degree of astigmatism where the eye is better at focusing light in one meridian than it is at another. It is possible to combine the effect of any astigmatism with the overall focusing power of the eye as a spherical equivalent in diopters. There are two main types of surgical correction for moderate to high myopia; excimer laser and phakic intraocular lenses (IOLs). Excimer laser refractive surgery for myopia works by removing corneal stroma to lessen the refractive power of the cornea and to bring the image of a viewed object into focus onto the retina rather than in front of it. Phakic IOLs for the treatment of myopia work by diverging light rays so that the image of a viewed object is brought into focus onto the retina rather than in front of it. They can be placed either in the anterior chamber of the eye in front of the iris or in the posterior chamber of the eye between the iris and the natural lens.

Efficacy, predictability, and safety of wavefront-guided refractive laser treatment: metaanalysis

PURPOSE: To compare the efficacy, predictability, safety, and induced higher-order aberrations (HOAs) between wavefront-guided and non-wavefront-guided ablations.

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Summaries for consumers

Excimer laser versus phakic intraocular lenses for the correction of moderate to high short‐sightedness

Myopia is a condition in which the focusing power (refraction) of the eye is greater than that required for clear vision of distant objects. Myopia is a common cause of visual disability throughout the world. The World Health Organization (WHO) has grouped myopia and uncorrected refractive error among the leading causes of blindness and vision impairment in the world. The overall power of the lens that would be needed to correct the myopia is expressed in diopters (D) of a sphere. Most people have some degree of astigmatism where the eye is better at focusing light in one meridian than it is at another. It is possible to combine the effect of any astigmatism with the overall focusing power of the eye as a spherical equivalent in diopters. There are two main types of surgical correction for moderate to high myopia; excimer laser and phakic intraocular lenses (IOLs). Excimer laser refractive surgery for myopia works by removing corneal stroma to lessen the refractive power of the cornea and to bring the image of a viewed object into focus onto the retina rather than in front of it. Phakic IOLs for the treatment of myopia work by diverging light rays so that the image of a viewed object is brought into focus onto the retina rather than in front of it. They can be placed either in the anterior chamber of the eye in front of the iris or in the posterior chamber of the eye between the iris and the natural lens.

Deep anterior lamellar keratoplasty versus penetrating keratoplasty for treating keratoconus

We reviewed the evidence about the effect of deep anterior lamellar keratoplasty (DALK) (new technique) versus penetrating keratoplasty (standard technique) in people with keratoconus.

Endothelial keratoplasty versus penetrating keratoplasty for Fuchs endothelial dystrophy

We compared the benefits and harms of penetrating keratoplasty (PKP) and endothelial keratoplasty (EK) in people with Fuchs endothelial dystrophy (FED) to determine whether one is more effective or safer than the other.

See all (5)

More about Astigmatism

Photo of an adult

Other terms to know:
Cornea, Refractive Error, Retina

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