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Contact Lens Series Volume 1.iso
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00196_Field_196.txt
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1997-10-28
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599b
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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.