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00190_Field_190.txt
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1997-10-29
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KERATOMETER MEASURING TECHNIQUE
Converting from Diopters to Radii
Some keratometers have the power drums marked in diopters
only while others will give both dioptric and radius values.
Often in contact lens fitting you want to know the radius of
the cornea.
If your keratometer is only marked with dioptric values, you
can convert the dioptric value to radius by using the
following formula:
(1.3375-1.00)
radius (meters)= -------------
diopters
Usually you want the value in millimeters, to obtain the
millimeter value you can multiply the above result by 1000
or more easily use the following formula:
337.5
radius (mm)= --------
diopters
Most contact lens textbooks and manuals that come with the keratometer provide tables that have conversion tables
Contact lens laboratories often supply them.