Why It Is Done continued...
Visual field tests may be
- To check for vision loss in any area of your
- To screen for eye diseases, such as
macular degeneration and
glaucoma, which cause gaps in the visual
- To look for damage to the nerves of the eye following a
stroke, head injury, or other condition that causes
reduced blood flow to the brain.
Color vision tests may be
- As part of a routine eye
- To screen for or diagnose color
- To screen applicants for jobs in which color perception
is important, such as truck driving, electronics, or the military.
How To Prepare
No special preparation is required
before having vision tests. If you wear glasses or contact lenses, bring them
with you to the examination since the tests cannot be properly performed
without them. If you have a copy of your current eyeglass prescription, bring
it with you.
Many medicines may affect the results of vision
tests. Be sure to tell your health professional about all the over-the-counter
and prescription medicines you take.
Talk to your health
professional about any concerns you have regarding the need for vision tests,
how they will be done, or what the results will mean. To help you understand
the importance of these tests, fill out the
medical test information form(What is a PDF document?).
How It Is Done
Visual acuity testing
tests are used to evaluate eyesight. Several types of visual acuity tests may
- The Snellen test
checks your ability to see at distances. It uses a wall chart that has several
rows of letters. The letters on the top row are the largest; those on the
bottom row are the smallest.
- You will stand or sit
20 ft (6 m) from the chart and
be asked to cover one eye and then read the smallest row of letters you can see
on the chart. If you are unable to cover your eye, an eye patch will be placed
over your eye.
- Each eye is tested separately. You may be given a
different chart or asked to read a row backward to make sure that you did not
memorize the sequence of letters from the previous test.
- If you
wear glasses or contacts, you may be asked to repeat the test on each eye while
- Let your health professional know if you have trouble
reading the letters on one side of the row, or if some letters disappear while
you are looking at other letters. You may have a visual field problem, and
visual field tests may be needed.
- The E chart tests the
vision of children and people who cannot read. The E chart is similar to the
Snellen chart in that there are several rows, but all of the rows contain only
the letter E in different positions. The top row is the largest and the bottom
row of Es is the smallest. You will be asked to point in the same direction as
the lines of the E. Similar charts use the letter C or pictures. These charts
are also available in a handheld card.
- The Near test uses a small
card (Jaeger chart) containing a few short lines or paragraphs of printed text
to test your near vision. The size of the print gradually gets smaller. You
will be asked to hold the card about
14 in. (36 cm) from your face
and read aloud the paragraph containing the smallest print you can comfortably
read. Both eyes are tested together, with and without corrective lenses. This
test is routinely done after age 40, because near vision tends to decline as
you age (presbyopia).