A diopter is a unit of measurement of the refractive error. It may be a negative number (myopia, nearsightedness), or a positive number (hyperopia, farsightedness). A -1.00 diopter myope is able to see objects at 1 meter clearly. A -2.00 diopter myope is able to see objects at a ½ meter clearly. The greater the myopia, the strength of the lens in diopters needed to correct the refractive error, and the closer an object must be to be viewed clearly.
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