Astigmatism is a visual defect, so the image of a point appears more or less elongated. It is perhaps one of the visual defects less understandable to patients. When having it, the light rays from an object endlessly diverge: one or both principal meridians of the eye are nearsighted (myopic astigmatism) and one or both principal meridians are farsighted (hyperopic astigmatism).
Figure: normal eye is to the left and eye with astigmatism is to the right
When the light rays relative to the two meridians focus respectively one in front and one behind the retina, we speak of mixed astigmatism. It can be combined in various ways with myopia and hyperopia producing complex defects.
The defect can be diagnosed by a routine eye exam, together with other visual defects such as myopia and hyperopia. It can be corrected with glasses, contact lenses or refractive surgery. The astigmatic subject uses cylindrical lenses (toric) that correct only the ametropic axis and have neutral power on the emmetropic axis.
Modern laser refractive surgery with LASIK technique can correct this defect thereby reducing or eliminating the need to use glasses or contact lenses.
Where it is not possible to perform an operation with a laser, an alternative is the use of premium intraocular lenses. Solutions with contact lenses or glasses may have drawbacks especially for those doing sports.