Astigmatism
Causes, Symptoms, and Treatment Options
Astigmatism is a vision condition that causes blurred vision due to an irregular shape of the cornea (the clear front cover of the eye) or by a curvature of the lens inside the eye. An irregular shaped cornea or lens prevents light from focusing properly on the retina (the light sensitive surface at the back of the eye). This results in blurry vision at any distance.
Astigmatism is a very common vision condition. Most people have some degree of astigmatism. Slight amounts of astigmatism usually do not affect vision and do not require treatment. However, larger amounts cause distorted or blurred vision, eye discomfort, and headaches.
What Causes Astigmatism?
Your eye has two anatomical structures that focus images: the cornea and the lens. In an ideally shaped eye, each of these focusing elements has a perfectly smooth curvature, like the surface of a smooth ball.
A cornea or lens with the proper curvature, bends (or refracts) incoming light in the same way, creating sharply focused images on the your retina. However, if your cornea or lens is not uniform and smoothly curved, light rays focus unevenly and create a refractive error. Astigmatism is a type of refractive error.
In astigmatism, your cornea or lens curves more steeply in one direction or another. When your cornea is misshapen, it is a corneal astigmatism. When your lens is misshapen, it is a lenticular astigmatism. Either type of astigmatism can cause blurred vision and blurred vision can occur in one or more direction, (horizontally, vertically or diagonally).
Astigmatism may occur in combination with other refractive errors as well, such as:
- Nearsightedness (myopia) -- This occurs when your cornea has too much curvature or your eye is longer than normal. Instead of focusing precisely on your retina, light focuses in front of your retina, resulting in a blurry appearance of distant objects.
- Farsightedness (hyperopia) -- This occurs when your cornea has too little curvature or your eye is shorter than normal. The effect is the opposite of nearsightedness. When your eye is in a relaxed state, light focuses behind the back of your eye, making nearby objects blurry.
Astigmatism may be present from birth, or it may develop after an eye injury, disease or surgery. Astigmatism is not caused or made worse by reading in poor light, sitting too close to the television or squinting.
What Are the Symptoms of Astigmatism?
- Distortion or blurring of images at all distances
- Headache and fatigue
- Squinting and eye discomfort or irritation
How Is Astigmatism Diagnosed?
The diagnosis of astigmatism is performed through a routine, comprehensive eye exam. Testing for astigmatism measures how the eyes focus light and determines the power of any optical lenses needed to compensate for reduced vision. This examination may include:
- Visual Acuity -- This exam determines how well you can see the details of a word or symbol from a specific distance away.
- Keratometry -- This diagnostic test measures the curvature of the anterior surface of the cornea, particularly for assessing the extent and axis of astigmatism.
- Refraction -- This eye exam measures a person's prescription for eyeglasses or contact lenses.
Using the information obtained from these tests, your vision professional can determine if you have astigmatism. These findings, combined with those of other tests performed, will allow the optometrist to determine the power of any lens correction needed to provide clear, comfortable vision and discuss options for treatment.
What Are the Treatment Options for Astigmatism?
If the degree of astigmatism is slight and there are no other problems of refraction (such as nearsightedness or farsightedness), treatment is not necessary. If the degree of astigmatism is great enough to cause eyestrain, headache or distortion of vision, your eye doctor may prescribe corrective lenses for clear and comfortable vision. Lastly, refractive surgery may be an option for correcting some forms of astigmatism.
If you think you may have astigmatism or another type of vision disorder, schedule an appointment with your local Vision Source eye professional today for a comprehensive eye exam and diagnosis.