In a perfect world, your eyes are perfectly round and focus light clearly and evenly. But if you have astigmatism, your cornea -- the clear dome that covers your iris and pupil -- is slightly warped.
As a result, light doesn’t bend light the way it should when it enters your eye. That makes things look blurry.
Most with astigmatism are born with it, and no one knows what causes it. If it comes on later, it could result from eye injury or disease.
A diagnosis starts with a visit to the eye doctor. If you’re an adult, you’re probably there because you noticed blurry vision. If you think your child has it, you likely found out from a vision test at her school.
Diagnosis: Eye Tests
The doctor may use one of these tests to diagnose astigmatism and figure out how severe it is:
Vision test. You’ll read the letters on a standard eye chart from 20 feet away. If your vision is 20/20, you can see from 20 feet what a normal eye can see from 20 feet. If your vision is 20/80, you must be 20 feet away to see what a normal eye sees from 80 feet away.
Refraction. The doctor will swing that big lens machine (it’s called a phoropter) in front of your face. You’ll look through it and tell him which lens choice helps you see the best. That’s how he figures out your prescription.
Sometimes, the doctor looks at your eye through a handheld device called a retinoscope. He may also use handheld lenses. Then he’ll offer you different choices in lenses through the phoropter to refine the fix until you can see the vision chart clearly. After he measures both eyes, he’ll give you a prescription for glasses or contacts.
Keratometry. This machine measures the bend in the center of your cornea. It determines the steepest and the flattest curves. The measurements tell your doctor about the shape of your cornea and how well it can focus. The doctor also uses the keratometer to fit contact lenses and to check your cornea after eye surgery.
Corneal topography. This advanced technology provides the most detailed information about your cornea’s shape. The doctor will tell you to look at something specific. Meanwhile, the device collects thousands of tiny measurements. A computer then builds a color map of your cornea from the data. Your doctor will refer to it if he plans surgery for astigmatism or cataracts. He might use it to fit your contacts. It can also help diagnose keratoconus, a disease that causes large amounts of astigmatism.
How Is Astigmatism Treated?
Your eye doctor can correct it with glasses, contact lenses, or surgery. But some doctors believe very small amounts of astigmatism are best left untreated.
Eyeglass lenses are curved to counteract the shape of the cornea or lens that's causing blurred vision. They work well when you look straight ahead. But depending on how much correction you need, they might make the floor or walls look tilted. This should go away as you get used to them. If you have severe astigmatism it might take a week or so. If your sight doesn’t get better, ask your doctor to recheck your prescription.
Contact lenses can also help, but you’ll need a special pair. All contacts rotate when you blink. The soft lenses used for astigmatism, called toric lenses, are designed to return to the same spot each time. Rigid (hard) gas permeable contact lenses are a better choice if your astigmatism is severe.
Laser eye surgery ( LASIK ) reshapes your cornea so it can focus light rays better. The doctor numbs your eye with drops, then uses a sterile mechanical device (or another laser) to create a thin flap on your cornea. He pulls it back with a tiny tool to expose the central layers of your cornea. He’ll use a laser to sculpt them. Then he returns the flap to its original position. Finally, he’ll give you anti-inflammatory and antibiotic eyedrops. Once he covers your eyes with transparent shields, you're ready to go home.
Most people who have LASIK are happy with the results. But there are some downsides to LASIK:
- The procedure could over- or under-correct your vision, which will require follow-up surgery.
- You may see a glare around lights at night. But new procedures and screening tests are designed to minimize glare.
- You may have increased eye dryness.
- If you’re 40 or older, you may still have to wear reading glasses. You can avoid this with a monovision technique that focuses one eye for distance and the other eye for near vision. You might think this would be confusing, but most people adjust easily. You can wear contact lenses or handheld lenses to see what it’ll be like before you get the surgery.
Astigmatic keratotomy, or limbal relaxing incisions, is another option. The surgeon makes tiny cuts on the steepest curves of your cornea. This lets light focus more precisely on your retina. If you have more severe astigmatism, you may have laser surgery instead.
How Can I Prevent It?
There’s no known way to prevent astigmatism.