Astigmatism is a condition of the human eye which causes either blurred vision or a sense that each eye is seeing objects slightly differently. Sometimes astigmatism can be detected by an individual if he covers one eye to look at an object, and then changes to cover the other eye. By switching back and forth between covering each eye while looking at the single object or in one direction, it will become apparent with astigmatism that the object seems to move, as though each eye is seeing it in a slightly different location.

Astigmatism is not a vision problem, but a structural problem with the eye. The human eye is usually shaped in a sphere, like a ball, but with astigmatism, the cornea of the eye is curved instead into an oval shape, more like a football. When the eye is not curved properly, or has uneven curves like a football, light will not travel in and out of the eye normally. Astigmatism causes light to bounce unevenly off the flat and steep curves of the oval shaped eye, thus allowing light to more than one point in the eye. This impairs focusing ability, causing blurred vision.

There are several ophthalmological tests to determine the presence and level of astigmatism. A keratometer and a corneal topographer measure the curvature of the cornea. An autorefractor can give an estimate of the eye's ability to focus light properly. Most ophthalmologists and optometrists are able to detect even slight cases of astigmatism with just a simple eye exam.

Glasses or contact lenses can be presecribed to treat astigmatism, but they generally do not correct the condition. Often, two different lenses will help the eyes focus together, thus offsetting the uneven focusing caused by astigmatism. Astigmatism, however, can be corrected with surgery. Lasik and astigmatic keratotomy are two commonly used surgeries for astigmatism. The object of surgery is to reshape the cornea of the eye and make it more spherical.

Astigmatism is quite common, with thirty percent of the population having some level of cornea curvature. Often, mild astigmatism goes largely unnoticed, but severe astigmatism may cause, in addition to blurred vision, headaches, squinting and fatigue. Most people with astigmatism are born with it, but the awareness of it increases with age.