Astigmatism
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Astigmatism is a refraction error of the eye characterized by an aspherical cornea in which one axis of corneal steepness is greater than the perpendicular axis. Astigmatism causes difficulties in seeing fine detail, and can be often corrected by glasses with a cylindrical lens (i.e. a lens that has different radii of curvature in different planes), contact lenses, or refractive surgery.
Astigmatism occurs when either the cornea or the lens of the eye is not perfectly spherical. As a result, the eye has different focal points in different planes. For example, the image may be clearly focused on the retina in the horizontal plane, but in front of the retina in the vertical plane.
In some cases vertical lines i.e. walls, may appear to the patient to be leaning over like the tower of Pisa.
Types of Astigmatism
- Simple
- Simple hyperopic astigmatism
- Simple myopic astigmatism
- Compound
- Compound hyperopic astigmatism
- Compound myopic astigmatism
- Mixed astigmatism
See also
- Eye
- Eyeglass prescription
- Hyperopia
- Lens (optics)
- Myopia
- Ophthalmology
- Optician
- Optometry
- Presbyopia
External links
- Astigmatism (http://www.eyetopics.com/Articles/45/1/Astigmatism.aspx)
- MedlinePlus article (http://www.nlm.nih.gov/medlineplus/ency/article/001015.htm)
- AllAboutVision.com article (http://www.allaboutvision.com/conditions/astigmatism.htm)
- hazabar.com article (http://www.habazar.com/opticaldirectory/Astigmatism.htm)
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