What Is Astigmatism?
Ideally, an eyeball is shaped like a perfectly round ball. Light comes into it and bends evenly, which gives you a clear view. But if your cornea is shaped more like a football, light gets bent more in one direction than another. That means only part of an object is in focus. Things at a distance may look blurry and wavy.
It’s common to have astigmatism along with nearsightedness (myopia) or farsightedness (hyperopia). These three conditions are called refractive errors because they involve how your eyes bend (refract) light.
Astigmatism is fairly easy for an eye doctor to fix with glasses, contacts, or surgery.
Symptoms of astigmatism may include:
Most people are born with it, but experts don’t know why. You can also get it after an eye injury, an eye disease, or surgery.
Rarely, a condition called keratoconus can cause astigmatism by making the clear front part of your eye (your cornea) thinner and more cone-shaped. You’ll probably need contacts (but not glasses) to see clearly.
You can’t get astigmatism from reading in low light or sitting too close to the TV.
Astigmatism symptoms come on slowly. Go to an eye doctor if you notice changes in your vision. You’ll need a complete eye exam. Your doctor will test the sharpness of your eyesight by asking you to read an eye chart. They’ll also use tools to measure your vision, including:
Phoropter. You look through a series of lenses to find the ones that give you the clearest vision.
Keratometer. This machine measures the bend in the center of your cornea. It finds the steepest and flattest curves. The measurements tell your doctor about the shape of your cornea and how well it can focus.
Autorefractor. This device shines light into your eye and measures how it changes as it bounces off the back. This gives your doctor an idea of which lenses you need.
Corneal topographer. This technology gives the most detailed information about your cornea’s shape. The doctor tells you to look at a specific point. Meanwhile, the device collects thousands of tiny measurements. A computer builds a color map of your cornea from the data. Your doctor will refer to it if they plan surgery for astigmatism or cataracts. They might use it to fit contacts. It can also help diagnose keratoconus.
Astigmatism Prescription Measurements
Your prescription will have some letters and numbers. OD means oculus dexter, your right eye, and OS is oculus sinister, your left eye. OU means oculus uterque, or both eyes.
The numbers are measurements called diopters.
- The first number is for something called spherical correction. If it has a minus sign, you’re nearsighted. If there’s a plus sign, you’re farsighted. A higher number means blurrier vision.
- The second numbers are your cylindrical correction. This is how strong your astigmatism is.
- The third one is the axis, the location of the astigmatism on your cornea.
For example, a prescription of “OD -1.00 x -2.00 x 155” means your right eye has 1 diopter of nearsightedness and 2 diopters of astigmatism at 155 degrees on your cornea.
Glasses or contacts can correct almost all cases of astigmatism. But if you have only a slight astigmatism and no other vision problems, you may not need them.
If you have a common level of astigmatism, you’ll probably have corrective lenses, like glasses or contacts, or surgery.
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 effect should go away as you get used to them. If you have severe astigmatism, it might take a week or so. Start by wearing the glasses first thing in the morning, for a few hours at a time, and adjusting slowly. If your vision doesn’t get better, ask your doctor to check 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. Doctors can use them for your regular contacts or for a procedure called orthokeratology. You wear the lenses while you sleep, and they reshape your cornea. You’ll need to keep wearing the lenses to hold this new shape, but you won’t have to wear them as often.
Laser eye surgery (LASIK or PRK) reshapes your cornea so it can focus light rays better. The doctor numbs your eye with drops and uses a sterile mechanical device (or another laser) to make a thin flap on your cornea. They pull it back to expose the central layers of your cornea and use a laser to sculpt them. Then, they return the flap to its original position. Finally, they give you anti-inflammatory and antibiotic eye drops. Once they cover your eyes with transparent shields, you're ready to go home.
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.
Astigmatism in Children
Many infants are born with astigmatism, and it often goes away before their first birthday. A child with an untreated vision condition might have a hard time at school. This could lead to an incorrect diagnosis of a learning disorder.
Because children usually can’t tell that there’s a problem with their vision, they need regular eye exams starting about 6 months of age.
There’s no known way to prevent astigmatism. If you’re at risk for keratoconus, it’s best not to rub your eyes as much as you can.