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Causes of Astigmatism



The causes of astigmatism usually have to do with the structure of the eye. The cornea and the lens are two very important parts of the eyes and both of them are used to focus on objects for creating perfect images. When the eyes are perfect, both the cornea and lens have the same smooth curvature, but in case the curvature of either the lens or the cornea bends, the image may not be completely focused. This is because the flat or steep curvature may refract the incoming light improperly, therefore impairing the sharply focused image and causing it to blur when it is formed at the retina.

Astigmatism is caused simply due to a refractive error. If the astigmatism is caused due to an incorrect curvature of the cornea, it is known as “corneal astigmatism” and if the condition is caused due to incorrect curvature of the lens, it is known as “lenticular astigmatism”.

The symptoms in both the cases are the same. Sometimes the blurring is more in one direction than in the other. The blurring may be horizontal, vertical or diagonal.

While in most cases, astigmatism is caused due to birth defects in the eyes, it often occurs along with other sight and refractive problems. These are:

• Nearsightedness: Also known as myopia, this condition occurs when the cornea curves too much to be able to focus on objects lying far from the line of sight correctly. Nearsightedness may also occur when the eye is too long for its optical power. Both of these conditions may cause the light to refract and focus slightly in front of the retina, therefore causing blurring of the image.
• Farsightedness: This is similar to nearsightedness, only in this case, the cornea is not curved as much as it normally should be, or the eye itself is shorter than normal. This causes the refracted light to focus and form an image behind the retina, therefore causing the images of objects near the light of sight to become blurry.

Though most of the cases of astigmatism are right from the time of birth, many people develop the condition after experiencing an eye injury or a disease. Contrary to popular belief, astigmatism is neither caused, nor made worse due to sitting too close to the television, squinting and reading in poor light or in a moving vehicle.