Astigmatism: A common form of visual impairment in which part of an image is blurred, due to an irregularity in the curvature of the front surface of the eye, the cornea. The curve of the cornea is shaped more like an American football or a rugby ball rather than a normal spherical basketball. Light rays entering the eye there are not uniformly focused on the retina. Rays entering through the more-curved surface are focused before 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 you are looking at is in clear focus at any one time.
Astigmatism may be so slight that it causes no problems. Almost everyone has some degree of astigmatism. Significant astigmatism can cause headaches and eye strain and seriously blur vision. Astigmatism may contribute to poor school performance but is often not detected during routine eye screening in schools. It is a refractive error, an error of focusing, that may coexist with other refractive errors like near- sightedness or far-sightedness.
Astigmatism is corrected with slightly cylindrical lenses that have greater light-bending power in one direction than the other. Using these lenses elongates objects in one direction and shortens them in the other, much like looking into a distorting wavy mirror at a circus The elongated figures in the paintings of the great Spanish painter El Greco, it has been suggested, might have been painted while he wore lenses to correct astigmatism. This is clearly wrong since such lenses were not yet in use in El Greco's day (1541-1614) and without them, what an astigmatic saw would have been blurred, not elongated. X-rays also show that El Greco first sketched more normal figures and then elongated them for whatever effect, religious or artistic, he wished to achieve.
Astigmatism was, in fact, not recognized until the 19th century. Only thereafter were lenses devised to correct it. The word "astigmatism" comes from the Greek "a-" (without) + "stigma" (point) = "without a point" referring to there being no point of convergence for the light rays on the retina.
Source: MedTerms™ Medical Dictionary
Get breaking medical news.
 |
RxList does not provide medical advice, diagnosis or treatment. See additional information.
Updated & New