Astigmatism

Ideally, the shape of our eye should be round like a soccer ball. When this occurs, all the light rays from an object will meet at a single point on the retina. If a structural defect of the eye occurs, and the resulting shape of the eye is elliptical like an egg, then the light rays from an object will not meet in a single point on the retina. The rays appear to spread as a line in various directions and vision can be blurry, distorted, or shadowy at distance or near.

Correction for astigmatism is given in the form of a cylinder A cylindrical lens bends light along only one axis as only one of its axes is curved. Astigmatism is corrected by introducing a cylindrical lens of opposite refractive properties. The axis of the cylinder follows the longest axis of the eye. The power of the cylinder is perpendicular to the axis.
Example: -1.00 x 180. Patients may have a combination of astigmatism and spherical refractive error. In that case, the physician may correct the problem by combining a spherical lens with a cylindrical lens placed along the appropriate axis. Example: -2.00 / -1.00 x 180

With LASIK refractive surgery, the refractive error of astigmatism can be eliminated and vision restored by changing the cornea shape which is irregular or not smooth, into a cornea which is regular or smooth.