Refractive errors are just one potential cause of blurred vision, so it is important to have an examination right away if you are experiencing symptoms.

The four most common refractive errors are:

• Myopia (also called nearsightedness)
• Hyperopia (also called farsightedness)
• Astigmatism (distorted vision)
  
• Presbyopia (an aging eye)
  

It is possible to have more than one of these at once.

Myopia

A myopic eye is longer than normal or has a cornea that is too steep, so that the light rays focus in front of the retina. Close objects look clear, but distant objects appear blurred.

Hyperopia

A hyperopic eye is shorter than normal. Light from close objects cannot focus clearly on the retina. The words on a page will seem blurry, or it will be difficult to see to thread a needle.

Astigmatism

Astigmatism distorts or blurs vision for both near and far objects. It's almost like looking into a fun house mirror in which you appear too tall, too wide or too thin. When you have astigmatism, the cornea (the clear front window of the eye) curves more in one direction than in the other — like a football. A normal cornea is round and smooth, like a basketball. It is possible to have astigmatism in combination with myopia or hyperopia.

Presbyopia

You may start to notice presbyopia around the age of 40, when you may begin to find that you have hold reading materials farther away from your face in order to see them clearly. This familiar event is often the first sign of presbyopia, which, if left uncorrected, can cause eye fatigue and headaches.

Get more detailed information on refractive errors from EyeCare America.