Images of objects at a close as well as at a far distance appear distorted: A dot in real life will produce an image of a line. The reason for this distortion is the shape of the cornea which does not resembles a ball but rather an egg. As the result, light rays are bent in different directions and do not come to focus on one refractive point on the retina but at different points.

Astigmatism frequently occurs together with nearsightedness or farsightedness; its correction value is also indicated in diopter.

Astigmatism is corrected by reshaping the corneal surface into the shape of a ball, so that light rays come to focus at one point of refraction. For eye glasses, the correction is made with so-called cylinder glasses. The position in front of the eye needs to have a specifically defined direction. This is why the correction value for eye glasses and contact lenses is measured in diopter for the cylinder value and in degrees for the position of the cylinder axis. Your prescription would read, for example, cylinder value: cyl. 1.5 dptr, axis 0º.

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