Astigmatism

What Is Astigmatism?

Astigmatism is a condition in which your eye isn’t completely round. Almost all of us have it to some degree.

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 eye 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.

Astigmatism Symptoms

Symptoms of astigmatism may include:

 

Astigmatism Causes

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.

Astigmatism2

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 Diagnosis

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/topographer. This machine uses a circle of light to measure the curve of your cornea.
  • 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.

 

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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.

Astigmatism Treatment

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.

There are two treatments for the common levels of astigmatism:

  • Corrective lenses. That means glasses or contacts. If you have astigmatism, your doctor will probably prescribe a special type of soft contact lenses called toric lenses. They can bend light more in one direction than the other. If your case is more severe, you might get gas-permeable rigid contact lenses 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.
  • Refractive surgery. Laser surgery also changes the shape of your cornea. Types of refractive surgery include LASIK and PRK. You’ll need to have otherwise healthy eyes with no retina problems or corneal scars.

Irregular astigmatism is far less common and is linked to problems with your cornea, the front part of the eye. Keratoconus is one example.

Astigmatism in Children

Many infants are born with astigmatism, and it often goes away before their first birthday.

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. A child with an untreated vision condition might have a hard time at school, and this could lead to an incorrect learning disorder diagnosis.

WebMD Medical Reference Reviewed by Whitney Seltman on November 11, 2019

Sources

SOURCES:

Yanoff, M. Ophthalmology, Mosby, 2008.

MedlinePlus: "Vision Problems."

National Eye Institute: "Facts About Refractive Errors," “Astigmatism.”

American Academy of Ophthalmology: “What Causes Astigmatism?” “Astigmatism Diagnosis and Treatment,” “What Do Astigmatism Measurements Mean?”

American Optometric Association: “Astigmatism.”

Mayo Clinic: “Astigmatism.”

Canadian Association of Optometrists: “How to Read Your Eyeglass Prescription.”

Boston Children’s Hospital: “Astigmatism.”

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