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Visual Acuity

Visual acuity is a measure of how well a person can focus on a distant object. To test visual acuity, the person may read letters or symbols on a wall chart (Snellen test) 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. A person who can read what people with normal vision can read at 20 ft (6 m) has 20/20 (6/6) 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).

ByHealthwise Staff
Primary Medical ReviewerKathleen Romito, MD - Family Medicine
Specialist Medical ReviewerChristopher J. Rudnisky, MD, MPH, FRCSC - Ophthalmology
Last RevisedJune 24, 2011

WebMD Medical Reference from Healthwise

Last Updated: June 24, 2011
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