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visual acuity

visual acuity is a measure of how well a person can focus on an object. to test visual acuity, the person may read letters or symbols on a chart from the top down, line by line, covering first one eye and then the other.

a visual acuity score is a ratio comparing the person's performance to that of people who have "normal" vision.

for example, a person who can read what people with normal vision can read at 20 ft (6 m) has 20/20 (6/6) distance vision. the larger the second number, the worse the vision.

  • if vision is 20/40 (6/12), the person can read at 20 ft (6 m) what people with normal vision can read at 40 ft (12 m).
  • if vision is 20/60 (6/18), the person can read at 20 ft (6 m) what people with normal vision can read at 60 ft (18 m).

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