Astigmatism refractive error eye (1 résultats)

Taschenbuch. Etat : Neu. nach der Bestellung gedruckt Neuware - Printed after ordering - Please note that the content of this book primarily consists of articlesavailable from Wikipedia or other free sources online. Astigmatism is anoptical defect in which vision is blurred due to the inability of theoptics of the eye to focus a point object into a sharp focused image onthe retina. This may be due to an irregular or toric curvature of thecornea or lens. There are two types of astigmatism: regular andirregular. Irregular astigmatism is often caused by a corneal scar orscattering in the crystalline lens and cannot be corrected by standardspectacle lenses, but can be corrected by contact lenses. Regularastigmatism arising from either the cornea or crystalline lens can becorrected by a toric lens. A toric surface resembles a section of thesurface of an American football or a doughnut where there are tworegular radii, one smaller than another. This optical shape gives riseto regular astigmatism in the eye. The first spectacle lenses thatcorrected astigmatism were made in Philadelphia in 1841.…