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Keratom.DIr
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00196_Field_196.txt
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1997-10-29
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602b
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HOW THE KERATOMETER WORKS
To measure the image size, which is
directly related to the corneal radius,
the prisms that form the left and top
images can be moved forward and back.
As the prisms move they increase or
decrease the separation of the
deviated image from the central image.
The examiner moves the prisms by
rotating the power drums. When they
are moved to the point where the
sides of the images touch (plus signs
or minus signs overlap) the size of
the image is know and is converted
to a dioptric power by the markings
on the drum.