Snellen Test
for Visual Acuity
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What is the
test?
A Snellen test uses a chart with different sizes
of letters or forms to evaluate your visual acuity-that
is, the sharpness of your vision. The test shows
how accurately you can see from a distance.
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How
do I prepare for the test?
No preparation is necessary.
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What
happens when the test is performed?
You stand or sit at a specific distance from
the eye chart. Usually you are told to cover
one eye with a cardboard piece or with your hand
while you read letters with the other eye and
say them out loud for the doctor.
In an eye clinic, you may have a more sophisticated
version of this test in which you look at the
chart through different strengths of lenses (a
little bit like looking through a telescope)
so that your doctor can find the proper strength
of glasses or contact lenses for you. Sometimes
the Snellen chart you see in an eye clinic is
actually a reflection on a mirror from a projector
in the back of the room. This enables eye doctors
to use a variety of charts without you having
to move from your chair. The test takes only
a few minutes.
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What
risks are there from the test?
There are no risks.
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Must
I do anything special after the test is over?
No.
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How
long is it before the result of the test is
known?
You can find out immediately whether your vision
is normal ("20/20") or whether you have a vision
problem. Glasses do not correct every vision
problem, but an eye doctor can tell you if they
will help.
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