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What is Astigmatism?
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.
What Causes Astigmatism?
Astigmatism usually occurs when the front surface of the eye, the cornea, has an irregular curvature. The cornea should be smooth and equally curved in all directions. In astigmatism, the front surface of the cornea is more oval in shape than round. This abnormality may result in vision that is much like looking into a distorted, wavy mirror. The distortion results because of an inability to focus light rays to a point.
Astigmatism is not a disease nor does it mean that you have "bad eyes." It simply means that you have variation or disturbance in the shape of your cornea. Some studies quote that 90% of the human population has some level of astigmatism. Not all corneas are perfectly curved, just as sets of teeth are seldom perfectly aligned. There are many variations that might occur in the corneal surface. 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 has an inherited component (it runs in the family). For that reason, some people are simply more prone to develop astigmatism than others.
How Does Astigmatism Affect Sight?
To fully understand why astigmatism causes a disturbance in sight, it is helpful to understand the process of sight. The clear cornea is situated at the very front surface of the eye and enables light to enter the eye. At that point of entry, 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 further refines the refractive work begun by the cornea and directs that point of light towards a precise location on the retina. If light is not focused into that fine point, the image that reaches the retina cannot be clearly transmitted to the brain. When astigmatism is present, the surface of the cornea, instead of being spherical, is distorted. Therefore, light rays entering the eye are not focused into the fine point needed or clear vision. Rather, light is focused on two distinct points, neither of which may be on the retina, resulting in a blurred image. Vision is typically worst as light levels around you are changing, such as the twilight hours at the end of the day, or pre-dawn hours as sunrise is occurring.
Who Develops Astigmatism?
Astigmatism is a very common problem. Some experts agree that almost all persons have some degree of astigmatism, often present at birth. The degree of astigmatism may remain the same throughout life. It also may fluctuate slightly throughout life.
What Are The Symptoms of Astigmatism?
The symptoms of astigmatism include a distortion or blurring of images at all distances---nearby as well as distant. Even though vision may be fairly sharp, when slight degrees of astigmatism are present, the condition may cause headache, fatigue, squinting, and eye discomfort or irritation. Of interest to parents and those who work with children, astigmatism may contribute to poor school work but is often not detected during routine screenings in schools.
How is Astigmatism Diagnosed?
Astigmatism is diagnosed through the process of a comprehensive eye health examination that checks for near vision, distance vision and clarity of vision.
How is Astigmatism Treated?
Dr. Fife will recommend corrective eyewear to help the eye direct light in a more effective manner. If the degree of astigmatism is slight and no other problems of refraction 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. Astigmatism often occurs with other refractive conditions such as nearsightedness or farsightedness. The corrective lenses needed when astigmatism is present are called "cylinders" and have greater light bending power in one area of the lens than in others. Dr. Fife has performed precise tests during your comprehensive eye health examination to determine precisely the ideal lens prescription. If you are interested in contact lenses, astigmatism may mean that you will need specially shaped lenses to give the best vision possible.