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Visual Acuity

Definition

The visual acuity test is used to determine the smallest letters a person can read on a standardized chart or card held 14 - 20 feet away.

Alternative Names

Eye test - acuity; Vision test - acuity

How the test is performed

This test may be done in a health care provider's office, a school, a work place, or elsewhere. You will be asked to remove your glasses or contacts and stand or sit 20 feet from the eye chart. Keep both eyes open, you will gently cover one eye with the palm of your hand, a piece of paper, or a paper cup while you read out loud the smallest line of letters that you can see on the chart.

If you are not sure of the letter, you may guess. This test is done on each eye, one at a time. If necessary, it is then repeated while you wear your glasses or contacts. You may also be asked to read letters or numbers from a card held 14 inches from your face. This will test your near vision.

How to prepare for the test

No special preparation is necessary for this test.

How the test will feel

There is no discomfort.

Why the test is performed

The visual acuity test is a routine part of an eye examination or general physical examination, particularly if there is a change in vision or a problem with vision. In children, the test is performed to screen for any visual problems. Vision problems in young children can often be corrected or improved. Undetected or untreated problems may result in permanent damage to vision.

Normal Values

Visual acuity is expressed as a fraction. The top number refers to the distance you stand from the chart. This is usually 20 feet. The bottom number indicates the distance at which a person with normal eyesight could read the same line you correctly read. For example, 20/20 is considered normal. 20/40 indicates that the line you correctly read at 20 feet can be read by a person with normal vision from 40 feet away.

What abnormal results mean

Abnormal results may be a sign that you need glasses or contacts, or may mean that you have an eye condition that needs further evaluation by a doctor.

Related topics:

  • Farsightedness
  • Nearsightedness
  • Presbyopia

What the risks are

There are no risks.

Review Date: 1/21/2009

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Information developed by A.D.A.M., Inc. regarding tests and test results may not directly correspond with information provided by UCSF Medical Center. Please discuss with your doctor any questions or concerns you may have.