Vision test - acuity

Alternative names
Eye test - acuity; Visual acuity test

Definition
The visual acuity test measures the smallest letters that you can read on a standardized chart at a distance of 20 feet.

How the test is performed

This test may be done in a health care provider’s office, a school, a work place, or elsewhere. Stand behind a line 20 feet from the eye chart. Remove glasses or contacts. Keep both eyes open and 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 read on the chart.

If you are not sure of the letter, you may guess. This is repeated with the other eye. Repeat the procedure while wearing glasses or contacts.

How to prepare for the test
No special preparation is necessary for this test.

For children:
The preparation you can provide for this test depends on your child’s age, previous experiences, and level of trust. For specific information regarding how you can prepare your child, see the following topics:

     
  • Toddler test or procedure preparation (1 to 3 years)  
  • Preschooler test or procedure preparation (3 to 6 years)  
  • Schoolage test or procedure preparation (6 to 12 years)  
  • Adolescent test or procedure preparation (12 to 18 years)

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.

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 letters at 20 feet that could be read by a person with normal vision at 40 feet.

What abnormal results mean
Abnormal results may indicate that you need corrective lenses to obtain normal vision, or may indicate an eye condition requiring further evaluation.

Related topics:

     
  • Nearsightedness  
  • Farsightedness  
  • Presbyopia

What the risks are
There are no risks.

Johns Hopkins patient information

Last revised: December 6, 2012
by Simon D. Mitin, M.D.

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