What is 20/20 Vision?

20/20 vision means your eye can see what the average human eye sees clearly at 20 feet.

If your eye can perceive objects at 20 feet that the average eye must be at 15 feet to see as clearly, then that eye has 20/15 vision. You should be so lucky--most Americans are nearsighted or farsighted to some degree. That is, either they see near objects clearly but not distant objects (nearsightedness, or myopia) or vice versa (farsightedness, or hyperopia).

Refractive surgery can correct for myopic vision by changing the shape of the cornea. But with potential side effects, such as pain, light sensitivity and optical distortion, and a small risk of even more serious eye problems, I'll stick with spectacles.

• How the Human Eye Works
• Common Eye Diseases