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astigmatism |
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astigmatismAberration occurring in the lens of the eye. It results when the curvature of the lens differs in two perpendicular planes, so that rays in one plane may be in focus while rays in the other are not. With astigmatic eyesight, the vertical and horizontal cannot be in focus at the same time; correction is by the use of a lens that reduces the overall focal length of one plane so that both planes are seen in sharp focus. How to thank TFD for its existence? Tell a friend about us, add a link to this page, add the site to iGoogle, or visit webmaster's page for free fun content. |
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Mixed astigmatism or irregular astigmatism describes the unequal curvature of the cornea in which one principal meridian is myopic and the other is hyperopic. Indications include myopia, hyperopia, and astigmatism as well as ocular abnormalities such as irregular astigmatism and irregularities as a result of a prior refractive surgery. George Waring's research related to the classification of normal corneal topography, which indicated that nearly 40 percent of the typical population has irregular astigmatism problems that would significantly benefit from topography-planned ablations. |
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