Astigmatism is a common eye problem that can make your vision blurry or distorted. It happens when your cornea (the clear front layer of your eye) or lens (an inner part of your eye that helps the eye focus) has a different shape than normal.

The only way to find out if you have astigmatism is to get an eye exam. Eyeglasses or contact lenses can help you see better — and some people can get surgery to fix their astigmatism.

Refraction is the bending of light as it passes through one object to another. Vision occurs when light rays are bent (refracted) as they pass through the cornea and the lens. The light is then focused on the retina. The retina converts the light-rays into messages that are sent through the optic nerve to the brain. The brain interprets these messages into the images we see.

Astigmatism is a common type of refractive error. It is a condition in which the eye does not focus light evenly onto the retina, the lightsensitive tissue at the back of the eye.

At a glance: Refractive Errors

• Types:

  Nearsightedness (myopia), farsightedness (hyperopia), astigmatism, presbyopia

• Most Common Symptom:

  Blurred vision

• Diagnosis:

  Eye exam

• Treatment:

  Eyeglasses, contact lenses, surgery

What are refractive errors?

Refractive errors are a type of vision problem that makes it hard to see clearly. They happen when the shape of your eye keeps light from focusing correctly on your retina (a light-sensitive layer of tissue in the back of your eye).

Refractive errors are the most common type of vision problem. More than 150 million Americans have a refractive error — but many don’t know that they could be seeing better. That’s why eye exams are so important.

If you have a refractive error, your eye doctor can prescribe eyeglasses or contact lenses to help you see clearly.

Astigmatism happens when your cornea or lens has a different shape than normal. The shape makes light bend differently as it enters your eye, causing a refractive error.

Doctors don’t know what causes astigmatism, and there’s no way to prevent it. Some people are born with astigmatism, but many people develop it as children or young adults. Some people may also develop astigmatism after an eye injury or an eye surgery.

Astigmatism occurs when light is bent differently depending on where it strikes the cornea and passes through the eyeball. The cornea of a normal eye is curved like a basketball, with the same degree of roundness in all areas. An eye with astigmatism has a cornea that is curved more like a football, with some areas that are steeper or more rounded than others. This can cause images to appear blurry and stretched out of shape enough to allow the eye to focus close objects clearly.

The most common symptoms of astigmatism are:

• Blurry vision
• Needing to squint to see clearly
• Headaches
• Eye strain
• Trouble seeing at night

If you have mild astigmatism, you might not notice any symptoms. That’s why it’s important to get regular eye exams — your eye doctor can help you make sure you’re seeing as clearly as possible. This is especially true for children, who may be less likely to realize that their vision isn’t normal.

It is possible to have mild astigmatism and not know about it. This is especially true for children, who are not aware of their vision being other than normal. Some adults may also have mild astigmatism without any symptoms. It’s important to have comprehensive dilated eye exams to make sure you are seeing your best.

Eye doctors can check for astigmatism as part of a dilated eye exam. The exam is simple and painless.

What is a dilated eye exam?

A dilated eye exam is the best thing you can do for your eye health! It’s the only way to check for eye diseases early on, when they’re easier to treat — and before they cause vision loss.

The exam is simple and painless. Your eye doctor will check for vision problems that make it hard to see clearly, like being nearsighted or farsighted. Then your doctor will give you some eye drops to dilate (widen) your pupil and check for eye diseases.

Since many eye diseases have no symptoms or warning signs, you could have a problem and not know it. Even if you think your eyes are healthy, getting a dilated eye exam is the only way to know for sure.

How often do I need to get a dilated eye exam?

How often you need a dilated eye exam depends on your risk for eye disease. Talk to your doctor about what’s right for you.

Get a dilated eye exam every 1 to 2 years if you:

• Are over age 60
• Are African American and over age 40
• Have a family history of glaucoma

If you have diabetes or high blood pressure, ask your doctor how often you need an exam. Most people with diabetes or high blood pressure need to get a dilated eye exam at least once a year.

What happens during a dilated eye exam?

The exam includes:

• A visual acuity test to check how clearly you see. Your doctor will ask you to read letters that are up close and far away.
• A visual field test to check your peripheral (side) vision. Your doctor will test how well you can see objects off to the sides of your vision without moving your eyes.
• An eye muscle function test to check for problems with the muscles around your eyeballs. Your doctor will move an object around and ask you to follow it with your eyes.
• A pupil response test to check how light enters your eyes. Your doctor will shine a small flashlight into your eyes and check how your pupils react to the light.
• A tonometrytest to measure the pressure in your eyes. Your doctor will use a machine to blow a quick puff of air onto your eye, or gently touch your eye with a special tool. Don’t worry — it doesn’t hurt!
• Dilation to check for problems with the inner parts of your eye. Your doctor will give you some eye drops to dilate (widen) your pupil. This helps the doctor see inside your eye.

Depending on your needs, your doctor may include other tests too. Ask your doctor if you have questions.

How does dilation work?

Dilating your pupil lets more light into your eye — just like opening a door lets light into a dark room. Dilation helps your eye doctor check for many common eye problems, including diabetic retinopathy, glaucoma, and age-related macular degeneration (AMD).

What happens after a dilated eye exam?

For a few hours after a dilated eye exam, your vision may be blurry and you may be sensitive to light. Ask a friend or family member to drive you home from your appointment.

If your eye doctor finds refractive errors in your vision, you may get a prescription for eyeglasses or contact lenses to help you see more clearly.

Bring your sunglasses!

Your eyes may be sensitive to light for a few hours after your exam. Sunglasses can help, so bring them if you have them! Your eye doctor may also have disposable sunglasses they can give you.

If your eye doctor finds signs of an eye disease, you can talk about treatment options and decide what’s right for you.

If you’re seeing clearly and there are no signs of eye disease, you’re all set until your next exam. Make an appointment for your next dilated eye exam before you leave the office — that way, you won’t forget!

The most common treatments for astigmatism are eyeglasses or contact lenses. Your eye doctor will prescribe the right lenses to help you see as clearly as possible.

Doctors can also use surgery to treat astigmatism. The surgery changes the shape of your cornea so that it can focus light correctly.

If your astigmatism is mild, you may not need treatment. Your eye doctor can help you figure out if you need to get treated, and what type of treatment is best for you.

How is astigmatism corrected?

Astigmatism can be corrected with eyeglasses, contact lenses, or surgery. Individual lifestyles affect the way astigmatism is treated.

• Eyeglasses are the simplest and safest way to correct astigmatism. Your eye care professional will prescribe appropriate lenses to help you see as clearly as possible.
• Contact Lenses work by becoming the first refractive surface for light rays entering the eye, causing a more precise refraction or focus. In many cases, contact lenses provide clearer vision, a wider field of vision, and greater comfort. They are a safe and effective option if fitted and used properly. However, contact lenses are not right for everyone. Discuss this with your eye care professional.
• Refractive Surgery aims to change the shape of the cornea permanently. This change in eye shape restores the focusing power of the eye by allowing the light rays to focus precisely on the retina for improved vision. There are many types of refractive surgeries. Your eye care professional can help you decide if surgery is an option for you.