What Are the Causes of Astigmatism?

Astigmatism causes blurred vision even when the patient is not nearsighted or farsighted. This common condition is a result of how the lens of the eye or cornea are shaped. If the patient and his doctor are aware that he has astigmatism, his vision can be corrected.

Heredity

• Astigmatism is a condition causing refractive errors in vision. "Refractive" refers to how the eyes bend light in order to see clearly. The astigmatic patient sees an object through what seems to be a wavy lens because the light entering the eye is not focused equally in all directions. Most people have some degree of astigmatism, which tends to be inherited.

Corneal/Lens Shape

• In astigmatism, the cornea is not shaped like a basketball, but it is shaped more like a football. Because of this, the eye is not able to focus light and objects on a single point on the retina. Instead, the light and the object are out of focus and blurred. In other cases, astigmatism results because of an irregularly shaped lens in the eye (not the cornea). If the patient is experiencing astigmatism because of a problem with the lens, she will experience blurred vision just as the person with the irregularly shaped cornea.

Injury/Surgery

• If an eye patient who never suffered from astigmatism has an injury to his eye or undergoes eye surgery, he may develop a subsequent astigmatism. He could notice that, despite what he does, if he is wearing eyeglasses that were prescribed before his injury or surgery, his vision is still blurred. This is because of the new way his eyes focus light and objects onto his retina and he will need to undergo a new eye exam to determine the degree of refractive error; the new prescription will need to allow for this so he can see correctly. Contact lenses that correct astigmatism (not a cure) will help him see clearly.

Keratoconus

• The eye patient who previously did not have astigmatism may develop this problem if she develops an eye disease called "keratoconus," which causes the cornea to become thinner and more cone-shaped. Fortunately, this eye condition is not very common. Still, she will notice her vision has become much worse, more blurred and it will not be possible to correct with glasses; contact lenses will be much more helpful for correcting her vision, but she may require a corneal transplant in the future.

Near/Farsighted

• Astigmatism is associated with nearsightedness, which is called "myopia," and farsightedness, called "hyperopia." When the eye patient is near or farsighted and suffers from astigmatism, he has what is called "refractive errors" because they interfere with how his eyes refract, or bend light. Having astigmatism simply means his eye doctor will have to correct for the curvature of his cornea or lens. Eyeglasses or contacts prescribed to correct both conditions will help him to see more clearly.