Astigmatism is a common type of visual problem that partly blurs an image. This is because there is irregularity in the curve of the front surface of the eye (the cornea). The cornea is curved more like a football (an American football, that is) or a rugby ball rather than the normal shape of a spherical basketball.
Light rays entering the astigmatic eye are not uniformly focused on the retina. Rays going through the more-curved surface are focused in front of the rays coming through the less-curved surface.
The light is focused clearly along one plane but is blurred along the other. The result is blurred vision at all distances. Only part of what an individual with an astigmatism is looking at is in clear focus at any given time.
Astigmatism may be so slight that it causes no problems. Almost everyone has some degree of astigmatism.
Moderate astigmatism can cause headaches and eye strain. Severe astigmatism can seriously blur vision. Astigmatism can contribute to poor school performance but paradoxically it is usually not detected during routine eye screening in schools.
Astigmatism is a refractive error. It may be present along with other problems in refraction, such as near- sightedness or far-sightedness.