You should have a distance test card placed at a distance of
twenty feet from the person you are examining, and in a good light.
A distance test card consists of letters of various sizes which it has
been found can be seen at certain distances by people with good
vision. Thus the largest letter is marked with a cc, meaning that this
should be seen at two hundred feet, and another line, XX, at twenty
feet, which is the proper distance for testing vision for distance,
for the reason that a normal eye is at rest when looking at any object
twenty feet from it or beyond, and the rays coming from it are
parallel and come to a focus on the retina. You must also have a near
vision test card with lines that should be seen by a normal eye from
ten to seventy-two inches, and a card of radiating lines for
astigmatism. With this preparation you are ready to proceed. To
illustrate, the first customer comes and tells you that up to six
months ago he had very good vision, but he finds now that, especially
at night, he has trouble in reading or writing, and that he finds he
can see better a little farther away. His head aches and eyes smart.
You will of course say that this is a very simple case.
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