Causes of Astigmatism

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Astigmatism is an eye problem or condition in which a person has blurred vision because of an eye problem. In this situation, the front exterior of the eye does not have the accurate curve in the cornea of the eye. The curve is irregular with one-half of the cornea being flatter or steeper than the other half. The distorted image results because the rays of light entering the eye do not focus correctly on the retina.
Astigmatism occurs in both children and adults. In addition, it happens frequently, but it is not contagious. It usually is present at birth but can result following eye surgery or after an eye injury. These eye problems are part of classifications of eye conditions known as refractive errors: hypermetropia or far-sightedness, myopia or shortsightedness and presbyopia or aging of the eye's lens.
Astigmatism takes two common forms. Corneal astigmatism occurs when the cornea is unevenly shaped and lenticular astigmatism when the lens is irregularly shaped.
In corneal astigmatism, the cornea is irregularly shaped. The cornea, which is a clear coating of tissue that covers the front of the eye, transmits and focuses light in the eye as well as protecting the eye from becoming infected and from damage. The cornea has to be perfectly curved to refract or bend light correctly as it enters the eye.
When the cornea does not have a perfect curve, the light is not refracted correctly and results in the retina receiving a distorted image. Consequently, the result will be imprecise vision or astigmatism in that eye.
People who have astigmatism often have a cornea, which is oval instead of a perfect circle. When the cornea’s arc is oblong, the light rays concentrate on two points within the retina.
Specialists are uncertain as to why some people have a cornea that is not curved correctly at birth. Some reports reveal that babies have a greater chance of astigmatism if the parents also have the condition. A higher proportion of babies who are born prematurely or with a lower body weight have astigmatism as compared with other babies.
Lenticular astigmatism is similar to corneal astigmatism but occurs in the lens instead of the cornea. The lens’ curvature varies instead of being perfect. The images at the back of the eye at the retina are distorted. Many of the patients who have lenticular astigmatism have a cornea with a normal shape. The imperfection is in the curve of the lens.
People who are diabetic develop lenticular astigmatism when higher levels of blood sugar produce a change in the shape of the lens. The change occurs slowly. It is identified at the time the patient begins the diabetic treatment. As the treatment controls the diabetes near normal levels, the shape of the lens returns to the regular level but may result in hypermetropia or far sightedness. It is often advised that those receiving diabetic treatments should wait for the lens to return to normal before receiving testing for new glasses.
Astigmatism also arises when the shape of the cornea is more oblong than it is round. The oval shape results in the rays of light focusing on two points in the back of the eye.
Sometimes astigmatism is caused by pressure of the eyelids on the cornea. It also can result from incorrect posture or use the eyes for detailed work. Some people inherit the problem.
Infrequently, astigmatism is caused by chalazia when the eye's lids swell or because of scars on the cornea. The scars may be caused by eye injury and the direction of light of the eye changes. It also may be owing to keratoconus, which is an uncommon condition in which a cornea changes from its normal round shape. Sometimes after eye surgery, a patient will develop astigmatism when the sutures are placed firmly produce the cornea to wrinkle, resulting in astigmatism until the injury is healed.