A refractive error is a condition caused by the shape of your eye that causes blurred vision. Nearsightedness, farsightedness, astigmatism and presbyopia are common refractive errors.

In a normal eye, light rays are bent (refracted) by the clear, outer covering of your eye (cornea) and the lens, then focused directly on the retina in the back of the eye. This results in clear vision. If you have a refractive error, light rays enter the eye in front of or behind the retina instead of directly on it, which causes blurred vision.

Refractive errors are very common — more than 150 million Americans have refractive errors.

Causes of refractive errors

Refractive errors are caused by having an abnormally shaped eyeball, which keeps you from focusing well. These abnormalities include:

  • Your eye is shorter or longer than normal
  • The shape of your cornea is not normal
  • The lens inside your eye changes shape with aging

Symptoms of refractive errors

Symptoms of the four common types of refractive errors include:

  • Nearsightedness (myopia): You can see objects clearly if they are close up, but faraway objects are blurry.
  • Farsightedness (hyperopia): You have clear vision at a distance, but close-up objects are blurry.
  • Astigmatism: Both faraway and up-close objects look blurry.
  • Presbyopia: As you age (usually after 40), you notice that close-up objects are harder to see.

Other symptoms of refractive errors include double vision, hazy vision, squinting, seeing a glare or halo around bright lights, and trouble focusing when reading.

Diagnosis of refractive errors

Your ophthalmologist or optometrist (eye doctor) will check for refractive errors as part of a comprehensive eye exam. Your doctor will ask you to read a vision chart while trying various lenses to find the best one to help you see clearly.

Part of a comprehensive exam includes dilating your eyes with eye drops so that your doctor can see inside your eyes. After your exam, you'll need sunglasses because your eyes will be sensitive to light for a few hours until your dilated pupils return to normal size.

Treatment of refractive errors

Your ophthalmologist or optometrist may suggest one or more of the following treatments:

  • Wearing glasses. This is the simplest and safest way to correct refractive errors.
  • Wearing contact lenses. These lenses sit on the surface of your eye and correct refractive errors.
  • LASIK surgery. This surgery uses a laser to change the shape of your cornea.
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