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Visual Acuity 

Units of Measure

Phil B. Fontanarosa

and Stacy Christiansen

Visual acuity should be reported on the basis of how the measurement was determined. For example, using the Snellen fraction with English units, 20/20 or 20/100 indicates that the person being evaluated can see at 20 ft what a person with “normal visual acuity” can see at 20 ft or at 100 ft, respectively. The equivalent metric measurements for visual acuity are 6/6 and 6/30, respectively. (See , Nomenclature, Ophthalmology Terms.)

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