Astigmatism (uh-STIG-muh-tiz-um) is a common and generally treatable imperfection in the curvature of your eye that causes blurred distance and near vision.
Astigmatism occurs when either the front surface of your eye (cornea) or the lens, inside your eye, has mismatched curves. Instead of having one curve like a round ball, the surface is egg shaped. This causes blurred vision at all distances.
Astigmatism is often present at birth and may occur in combination with nearsightedness or farsightedness. Often it's not pronounced enough to require corrective action. When it is, your treatment options are corrective lenses or surgery.
Signs and symptoms of astigmatism may include:
See an eye doctor if your eye symptoms detract from your enjoyment of activities or interfere with your ability to perform everyday tasks. An eye doctor can determine whether you have astigmatism and, if so, to what degree. He or she can then advise you of your options to correct your vision.
Children may not realize their vision is blurry, so they need to be screened for eye disease and have their vision tested by a pediatrician, an ophthalmologist, an optometrist or another trained screener at the following ages and intervals.
Your eye has two structures with curved surfaces that bend (refract) light onto the retina, which makes the images:
In a perfectly shaped eye, each of these elements has a round curvature, like the surface of a smooth ball. A cornea and lens with such curvature bend (refract) all incoming light to make a sharply focused image directly on the retina, at the back of your eye.
If either your cornea or lens is egg shaped with two mismatched curves, light rays aren't bent properly, causing a refractive error. This makes a blurry image. Astigmatism is a type of refractive error.
Astigmatism occurs when your cornea or lens is curved more steeply in one direction than in another. You have corneal astigmatism if your cornea has mismatched curves. You have lenticular astigmatism if your lens has mismatched curves.
Either type of astigmatism can cause blurred vision. Blurred vision may occur more in one direction, either horizontally, vertically or diagonally.
Astigmatism may be present from birth, or it may develop after an eye injury, disease or surgery. Astigmatism isn't caused or made worse by reading in poor light, sitting too close to the television or squinting.
Astigmatism may occur in combination with other refractive errors, which include:
Astigmatism is diagnosed by an eye exam. A complete eye exam involves a series of tests to check your eye health and a refraction, which determines how your eyes bend light. Your eye doctor may use various instruments, aim bright lights directly at your eyes and ask you to look through several lenses. Your doctor uses these tests to examine different aspects of your eyes and vision and to determine the prescription needed to provide clear vision with eyeglasses or contact lenses.