Astigmatism is a visual alteration caused by an irregularity of light refraction in the cornea or lens in a given two-dimensional plane. The consequence of this defect is the perception of distorted and blurred images, whether in far or near vision.

In the astigmatic eye, the light that strikes the cornea is refracted so that the images focus before or after the retina, depending on the magnitude of the change. This leads to distorted vision, rather like the mirrors seen at funfairs.

This visual irregularity is genetically predetermined. Apart from distorted vision, symptoms include frontal headaches and slight tilting of the head as the patient tries to find a more convenient angle for viewing.

At present, astigmatism can be corrected by wearing glasses or contact lenses, laser correction, or intraocular surgery. These different treatment modalities are adapted to different types of patients and to different types of refractive errors. However, in most people, the method that provides greater satisfaction, and more comfort and visual freedom, is laser correction surgery.