| Astigmatism (eye) |
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Information AboutAstigmatism (eye) |
In Ophthalmology , 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, non-figure of revolution Cornea in which the corneal profile Slope and refractive power in one meridian is greater than that of 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 Lens es, or Refractive Surgery . Astigmatism occurs when either the cornea or the Lens of the eye is not a Figure Of Revolution . 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 (sagittal) plane, but in front of the retina in the vertical (tangential) plane. In some cases vertical lines (e.g., walls) may appear to the patient to be leaning over like the Tower Of Pisa . TYPES OF ASTIGMATISM Based on asymmetry of structure
Based on axis of the principal meridians
Based on focus of the principal meridians
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 A recent Brazilian study found that 34% of the students in one city were astigmatic [http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=16059562&query_hl=7 . 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 astigmatism[http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=15177965&query_hl=20]. A recent Polish study revealed that "with-the-rule astigmatism" may lead to the onset of Myopia {Link without Title} . A number of studies have found that the prevalence of astigmatism increases with age {Link without Title} . DIAGNOSIS Symptoms Although mild astigmatism may be asymptomatic, higher amounts of astigmatism may cause symptoms such as blurry vision, squinting, asthenopia, fatigue, or headaches [http://www.medicinenet.com/astigmatism/article.htm {Link without Title} . Signs and tests There are a number of tests used by or Retinoscopy may provide an objective estimate of the eye's refractive error and the use of Jackson Cross Cylinder s in a Phoropter may be used to subjectively refine those measurements [http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=3808608&dopt=Abstract An alternative technique with the phoropter requires the use of a "clock dial" or "sunburst" chart to deterimine the astigmatic axis and power[http://www.quantumoptical.com/onlinecourses/nysso/brp/slide1.asp?courses=19 [http://www.nova.edu/hpd/otm/nbeo/refract1.htm]. TREATMENT Astigmatism may be corrected with eyeglasses, contact lenses, or refractive surgery. Various considerations involving ocular health, refractive status, and lifestyle frequently determine whether one option may be better than another. In those with Keratoconus , rigid gas permeable contact lenses often enable patients to achieve better Visual Acuities than eyeglasses. RELATED CONDITIONS SEE ALSO EXTERNAL LINKS |
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