The ABCs of Astigmatism
The blurry stop sign illustrates a very common vision problem. Many people have some degree of astigmatism. In fact, it is rare to find a perfectly formed eye. Astigmatism appears to run in families and is often present from birth. If you have astigmatism, chances are good your children will have it also. It may worsen slowly over time but may remain fairly stable throughout life. Astigmatism often occurs with other vision conditions such as nearsightedness (myopia) and farsightedness (hyperopia.)
What is it?
You may have heard astigmatism described as a condition in which the cornea resembles the shape of a "football" more than it does the shape of a basketball. When the cornea is more oval than round, light does not focus properly on the back of the eye (retina).
In the illustration, the cornea (in blue) has a different curvature vertically than it does horizontally. Vertical light rays (green) can be seen to focus in front of the retina, while the horizontal light rays (lavender) focus behind the retina. The difference in light focusing power between the vertical and horizontal is equal to the amount of the eye's astigmatism.
If your eyeglass prescription has three parts rather than one, you have some degree of astigmatism. A prescription with three parts might be: -2.00 -1.00 x 90. The first part (-2.00) indicates your nearsightedness; parts two and three indicate the amount and orientation of your astigmatism.
The most common symptom of astigmatism is blurred vision. Some people describe it as double vision but in only one eye. As a result of trying to focus on near or distant objects, a patient may develop eyestrain, squinting and headaches. Note the diagram at right - a person WITHOUT astigmatism would see all the radial lines as perfectly sharp and with the same contrast. The diagram illustrates how some lines might appear clearer than others to a person with astigmatism.
Children with astigmatism may be too young to notice or describe astigmatism. They may frown, squint, or pull objects close in an effort to get a clearer picture. They may also tilt or turn their head. This extra effort can lead to eyestrain, fatigue or reduced reading efficiency.
Glasses are a good, reliable choice for treating astigmatism. If treating a large amount of astigmatism, the doctor may not totally correct the astigmatism. The new prescription in the eyeglasses may initially make the floor appear to tilt, thus making it difficult for the patient to accept a full correction. The tilting often disappears after the new glasses have been worn exclusively for more than a few days. Switching back and forth between the new and an older pair of glasses can often increase the time required to adjust to the new prescription.
It is also possible to correct astigmatism using certain types of contact lenses. Patients who prefer contact lenses can generally be helped. Both gas permeable rigid and soft toric contacts are possible choices. In some cases, surgery may also be an option, especially for people who have dry eyes or other conditions that prohibit them from wearing corrective lenses. The most common type of surgery used to correct astigmatism is LASIK (laser in situ keratomileusis).
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. Your eye doctor can answer any questions you may have about the various methods for correcting astigmatism and other vision problems.