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 have conversion tables Contact lens laboratories often supply them.