Overview

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.

Source: http://www.mayoclinic.com

Symptoms

Signs and symptoms of astigmatism may include:

• Blurred or distorted vision
• Eyestrain or discomfort
• Headaches
• Difficulty with night vision
• Squinting

When to see a doctor

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 and adolescents

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.

• During the newborn period
• At well-child visits until school age
• During school years, every one to two years at well-child visits, at the eye doctor, or through school or public screenings

Source: http://www.mayoclinic.com

Causes

Your eye has two structures with curved surfaces that bend (refract) light onto the retina, which makes the images:

• The cornea, the clear front surface of your eye along with the tear film
• The lens, a clear structure inside your eye that changes shape to help focus on near objects

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.

A refractive error

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.

Other refractive errors

Astigmatism may occur in combination with other refractive errors, which include:

• Nearsightedness (myopia). This occurs when your cornea is curved too much or your eye is longer than normal. Instead of being focused precisely on your retina, light is focused in front of your retina, making distant objects seem blurry.
• Farsightedness (hyperopia). This occurs when your cornea is curved too little or your eye is shorter than normal. The effect is the opposite of nearsightedness. When your eye is in a relaxed state, light never comes to a focus on the back of your eye, making nearby objects seem blurry.

Diagnosis

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.

Source: http://www.mayoclinic.com