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).
| Author: | Jeannette Curtis |
| Medical Review: | Patrice Burgess, MD - Family Medicine Adam Husney, MD - Family Medicine Kathleen Romito, MD - Family Medicine |
| Last Updated: May 25, 2007 | |
© 1995-2012 Healthwise, Incorporated. Healthwise, Healthwise for every health decision, and the Healthwise logo are trademarks of Healthwise, Incorporated.
This information does not replace the advice of a doctor. Healthwise discalims any warranty or liability for your use of this information. Your use of this information means that you agree to the Terms of Use.