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detection of a target having two or more parts, often measured by using the Snellen test types; indicated by two numbers: the first represents the distance at which a patient sees the test types (usually 6 m. or 20 ft.), and the second, the distance at which the test types subtend an angle of 5 min.; for example, vision of 6/9 indicates a test distance of 6 m. and recognition of symbols that subtend an angle of 5 min. at a distance of 9 m.
Synonym(s): visual acuity