Eye test - acuity; Vision test - acuity; Snellen test
Visual acuity is expressed as a fraction.
For example, 20/20 is considered normal. 20/40 indicates that the line you correctly read at 20 feet away can be read by a person with normal vision from 40 feet away.
Even if you miss one or two letters on the smallest line you can read, you are still considered to have vision equal to that line.
Colenbrander A. Measuring vision and vision loss. In: Tasman W, Jaeger EA, eds. Duane's Ophthalmology. 15th ed. Philadelphia, Pa: Lippincott Williams & Wilkins; 2009:chap 51.
Miller D, Schor P, Magnante P. Optics of the normal eye. In: Yanoff M, Duker JS, eds. Ophthalmology. 3rd ed. St. Louis, MO: Mosby Elsevier;2008:chap 2.6.
American Academy of Ophthalmology Preferred Practice Patterns Committee. Preferred Practice Guidelines. Comprehensive Adult Medical Eye Evaluation. San Francisco, CA: American Academy of Ophthalmology, 2010. Accessed January 17, 2011.
© 2011 University of Maryland Medical Center (UMMC). All rights reserved.
UMMC is a member of the University of Maryland Medical System,
22 S. Greene Street, Baltimore, MD 21201. TDD: 1-800-735-2258 or 1.866.408.6885