Sunday, May 27, 2012

20-20 vision is based on the distance of 20 ... feet

When you do an eye test, the

distance between you and the
eye chart is 20 feet. The
distance was chosen because
the rays of light, as you
experience it from your two eyes, are about parallel to an
object at that distance. The
third line from the bottom on
the eye chart is the 20-20 line.
If you can see that line fine at
20 feet, you have 20-20 vision. If you have 20-10 vision, for
instance, you can spot letters
at a distance that others need
to stand at 10 feet to see.

The chart that is traditionally
used for eye test is the Snellen chart, named after Dutch ophthalmologist Hermann Snellen who developed the chart during 1862. To test a
person’s central visual field for
blind spots or distortion, the Amsler Grid is used.

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