Dictionary
(ophthalmology) impaired eyesight resulting usually from irregular conformation of the cornea common in nearsighted people (optics) defect in an optical system in which light rays from a single point fail to converge in a single focal point
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Wikipedia
DiseaseDisorder infobox
Name = Astigmatism
ICD10 = H52.2
ICD9 = 367.2
Astigmatism is a refraction error of the eye in which there is a difference in degree of refraction in different meridians. It is typically 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 Cylindercylindrical lens (optics)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 (vision)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 Leaning_Tower_of_Pisatower of Pisa.
Types of astigmatism - Types of astigmatism based on asymmetry of structure:Corneal astigmatism - astigmatism due to an irregularly shaped corneaLenticular astigmatism - astigmatism due to an irregularly shaped lensTypes of astigmatism based on axis of the principal meridians:Regular astigmatism:*Against-the-rule astigmatism:*With-the-rule astigmatism:*Oblique astigmatismIrregular astigmatismTypes of astigmatism based on focus of the principal meridians:Simple astigmatism*Simple hyperopic astigmatism*Simple myopic astigmatismCompound astigmatism*Compound hyperopic astigmatism*Compound myopic astigmatismMixed astigmatism Compact Disc players use an astigmatic lens for focusing. When one axis is more in focus than the other, dot-like features on the disc project to oval shapes. The orientation of the oval indicates which axis is more in focus, and thus which direction the lens needs to move. A square arrangement of only four sensors can determine this bias without being fooled by long pits.
Prevalence - According to an American study published in ''Archives of Ophthalmology'', nearly 3 in 10 children between the ages of 5 and 17 have astigmatism archopht.ama-assn.org. A recent Brazilian study found that 34% of the students in one city were astigmatic ncbi.nlm.nih.gov. Regarding the prevalence in adults, a recent study in Bangladesh found that nearly 1 in 3 (32.4%) of those over the age of 30 had astigmatismncbi.nlm.nih.gov.A recent Polish study revealed that "with-the-rule astigmatism" may lead to the creaton of myopia ncbi.nlm.nih.gov.A number of studies have found that the prevalence of astigmatism increases with agencbi.nlm.nih.gov.
See also - EyeEyeglass prescriptionHyperopiaKeratoconusLasikLens (optics)MyopiaOphthalmologyOpticianOptometryPresbyopia
External links - eyetopics.com - Astigmatism nlm.nih.gov - MedlinePlus article allaboutvision.com - AllAboutVision.com article habazar.com - hazabar.com article med-stub !Category:EyeCategory:Ophthalmo logyCategory:Visionde:Astigmat ismuses:Astigmatismoit:Astigma tismohe:אסטיגמציהja: 視pl:Astygmatyzmpt:Astigmat ismosv:Astigmatism
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