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Health A-Z

Medical Content Created by the Faculty of the
Harvard Medical School

What Happens During the Test?

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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From Health A-Z, Harvard Health Publications. Copyright 2007 by the President and Fellows of Harvard College. All rights reserved. Written permission is required to reproduce, in any manner, in whole or in part, the material contained herein. To make a reprint request, contact Harvard Health Publications. Used with permission of StayWell.

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