Astigmatism is a refractive eye condition when the eye does not form a point focus. This leads to distortion of viewed objects, much like viewing your reflection in the back of a spoon. Astigmatism results in difficulty seeing things when they are both near and far. This condition does not occur in isolation, but in combination with either myopia or hypermetropia.
Astigmatism is caused by non-rotational symmetry of the focussing power of the eye. It is typically caused by the curvature of the optical parts of the eye, either the cornea or crystalline lens, varying in different meridians. This can be likened to the uneven surface curvature of a rugby ball. Less commonly, astigmatism is caused by non-parallel alignment of the optical parts of the eye or the retina; or, alterations in the optical regularity of the lens within the eye that disturbs how it bends light due to cataract.
Hypermetropia is most commonly treated with spectacles that use lenses where at least one surface has an uneven curvature. It is critical that these lenses are orientated correctly so as provide good vision. Optical correction astigmatism usually gives normal vision.
It is possible to correct astigmatism with contact lenses, although this is necessarily more difficult than with spectacles because to provide clear vision the lens must not rotate excessively. Indeed, there is a conflict between the optical requirements for rotational stability and the physiological requirements for sufficient movement to avoid the build-up of corneal waste products that may lead to inflammation. A compromise must be made in the fitting of the contact lens, particularly for high degree of astigmatism when correct alignment is critical.
Refractive surgery alters the focusing parts of the eye. It normally does this by re-shaping the cornea using a laser, but alternatives include inserting a lens within the eye. As with any form of surgery these techniques can lead to complications, which include glare and reduced vision that are not correctable.