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If you experience a distortion or blurring of images at all distances -- nearby as well as far -- you may have astigmatism. Even if your vision is fairly sharp, headache, fatigue, squinting and eye discomfort or irritation may indicate a slight degree of astigmatism. A thorough eye examination, including tests of near vision, distant vision and vision clarity, can determine if astigmatism is present. Astigmatism is not a disease nor does it mean that you have "bad eyes." It simply means that you have a variation or disturbance in the shape of your cornea.
Astigmatism is one of a group of eye conditions known as refractive errors. Refractive errors cause a disturbance in the way that light rays are focused within the eye. Astigmatism occurs when the surface of the cornea is shaped more like the back of a spoon rather than a perfectly round surface, with greater curvature in one direction over the other. Astigmatism, which often occurs in combination with myopia and hyperopia causes multiple focal points with the eye resulting in a blurry or distorted vision. Astigmatism affects your vision at both near and far. Sometimes incorrectly called a "stigmatism," astigmatism is a common refractive error, like myopia and hyperopia. An irregularly shaped cornea is called astigmatism. Degrees of Astigmatism
Most people have some degree of astigmatism. Astigmatism occurs when the front surface of your eye (cornea) is slightly irregular in shape, resulting in vision being blurred at all distances. Astigmatism is not a disease, but is actually a vision condition that is quite common. When the front of your eye is more oval than round, light does not focus properly on the back of your eye (retina). The causes of this irregular shape are unclear. In some cases, it may be hereditary or it may result from such factors as pressure of the eyelids on the cornea, incorrect posture or an increased use of the eyes for close work.
Astigmatism usually occurs when the front surface of the eye, the cornea, has an irregular curvature. Normally the cornea is smooth and equally curved in all directions and light entering the cornea is focused equally on all planes, or in all directions. In astigmatism, the front surface of the cornea is curved more in one direction than in the other. With the cornea’s shape more like that of an American football or rugby ball than a basketball, the light hitting the more curved surface comes to a focus before that which enters the eye through the less curved surface. Thus, the light is focused clearly along one plane, but is blurred along the other so only part of anything being looked at can be in focus at any time. This abnormality may result in vision that is much like looking into a distorted, wavy mirror. The distortion results because of an inability of the eye to focus light rays to a point.
Why are corneas shaped differently? Not all corneas are perfectly curved, just as sets of teeth are seldom perfectly aligned. The degree of variation determines whether or not you will need corrective eyewear. If the corneal surface has a high degree of variation in its curvature, light refraction may be impaired to the degree that corrective lenses are needed to help focus light rays better. The exact reason for differences in corneal shape remains unknown, but the tendency to develop astigmatism is inherited. For that reason, some people are more prone to develop astigmatism than others. The retina is a paper-thin tissue that lines the back of the eye and sends visual signals to the brain. In the middle of the retina is a tiny area called the macula. The macula is made up of millions of light-sensing cells that help to produce central vision. How does astigmatism affect sight? The crystal clear cornea is situated at the very front surface of the eye and enables light to enter the eyeball. The cornea accomplishes about four-fifths of the refractive work needed for clear vision, bending light rays toward one another into a point. The lens, located behind the cornea, further refines the refractive work begun by the cornea and directs the point of light toward a precise location on the retina, known as the fovea. If light is not focused into a fine point on the fovea, the image that reaches the retina cannot be clearly transmitted to the brain. When astigmatism is present, the surface of the cornea is distorted instead of being spherical. It is unable to focus light rays entering the eye into the fine point needed for clear vision. At any time, only a small proportion of the rays are focused and the remainder are not, so that the image formed is always blurred. Usually, astigmatism causes blurred vision at all distances.
Very mild astigmatism may not even be noticed, or cause eye strain, headaches and slightly blurry vision. Severe astigmatism produces blurred or distorted vision.
Astigmatism is diagnosed in the course of a thorough eye examination. If the degree of astigmatism is slight and no other problems of refraction, such as myopia and hyperopia, are present, corrective lenses may not be needed. If the degree of astigmatism is great enough to cause eyestrain, headache, or distortion of vision, prescription lenses will be needed for clear and comfortable vision. Correction Your eye care professional will recommend corrective eyewear to help the eye direct light in a more effective manner. The corrective lenses needed when astigmatism is present are called Toric lenses and have an additional power element called a cylinder. They have greater light-bending power in one axis than in others. Your eye care professional will perform precise tests during your eye examination to determine the ideal lens prescription. Astigmatism may increase slowly. Regular eye care can help to insure that proper vision is maintained. You may have to adjust to wearing eyeglasses or contact lenses if you do not wear them now. Other than that, astigmatism probably will not significantly affect your lifestyle at all.
For more information of Astigmatism and its treatment/correction:
Source(s): All above information & images are based on: an article on astigmatism at cvworld.com, an article written by Gretchyn Bailey, allaboutvision.com and an article at LaserSurgeryForEyes.com. All rights reserved by respective owners. For our full credit and copyright information please view our Credit List.
Disclaimer: Any information displayed here is just for educational purposes, and may not be taken as an expert advice and should not be applied in life without consulting your eye doctor/specialist. We here by take no responsiblity of the accuracy of the above content as they have been taken from various sources. |
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