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Vision tests check many different functions of
the eye. The tests measure your ability to see details at near and far
distances, check for gaps or defects in your field of vision, and evaluate your
ability to see different colors.
Visual acuity tests may be done:
Refraction is done:
Visual field tests may be
Color vision tests may be
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?).
tests are used to evaluate eyesight. Several types of visual acuity tests may
If you cannot read any of the letters or print on these
charts because of poor vision, your visual acuity will be tested by other
techniques, such as counting fingers, detecting hand movements, or
distinguishing the direction or perception of light sources (such as room light
or a penlight held up close to the face).
Visual acuity tests
usually take about 5 to 10 minutes. They may be performed by a nurse, a medical
optometrist, a teacher, or some other trained person.
Testing may be done at a doctor's office, school, workplace, health fair, or
Refraction is a test that measures the
eye's need for a corrective lens (refractive error). For this test, you will be
asked to describe the effects of looking at an eye chart through various
Your health professional may use eyedrops to
widen (dilate) your
pupils before you start this test. The eyedrops take
about 15 to 20 minutes to dilate the pupil fully.
retinoscope, your health professional may shine light into your eyes. A series
of trial lenses will be placed in front of your eyes and adjusted until the
light rays are properly focused on your retina. Testing one eye at a time, the
health professional will ask you to compare the effects of two lenses (first
one lens, then the other). You should state which lens of each pair gives you
better vision. The health professional will continue to test your eyes with
different lenses until it is determined which lenses correct your vision the
Visual field tests are used to
check for gaps in your range of vision. They can help detect eye diseases or
nervous system problems that limit your ability to see objects clearly in the
entire visual field or in one part of it. Several tests are commonly done to
evaluate a person's visual field.
Color vision tests check your
ability to distinguish colors. In the most commonly used color vision test, you
look for different colored numbers or symbols hidden in varying backgrounds of
First, you are shown sample patterns and told what
symbols and numbers you can expect to see. You then sit at a table and cover
one eye. The health professional holds the color test patterns about
14 in. (36 cm) away from you.
Some patterns are harder to pick out than others. As the health
professional holds up a pattern, you will identify the number or symbol you see
and trace it using a pointer. Some patterns may not have a number or symbol.
The test is then repeated with the other eye.
You should not feel any discomfort
during these vision tests.
Dilating drops may make your eyes sting and cause a
medicine taste in your mouth. You will have trouble focusing your eyes for
up to 12 hours after your eyes have been dilated. Your distance vision usually
is not affected as much as your near vision, though your eyes may be very
sensitive to light. Do not drive for several hours after your eyes have been
dilated. Wearing sunglasses may make you more comfortable until the effect of
the drops wears off.
In some people, the dilating eyedrops can cause
Vision tests check many different
functions of the eye.
The visual acuity score
compares your distance vision with that of people who have normal vision, using
an eye chart. Each eye's score is expressed as two numbers, such as 20/20 (6/6)
or 20/100 (6/30). The first number is the distance you stand from the chart,
usually 20 ft (6 m) when using
a typical wall chart. The second number is the distance from which people with
normal eyesight can read the same line on the eye chart.
(6/6) vision is considered normal. A person with 20/20 vision can see at
20 ft (6 m) what people with
normal vision can see at this distance.
For near vision, 14/14 (35/35) is normal, with
14 in. (36 cm) being the normal
distance for reading. If the second number is greater than 14 (14/20, for
example, or 35/50), it means that you have reduced near vision. You have to be
14 in. (36 cm) away to read
print that people with normal near vision can read from
20 in. (51 cm).
Jaeger (J) number is another way to rate your near vision. The J number relates
to the size of text you could read on the Jaeger chart. The J number goes up as
the print size of the text you read goes up. The higher the J number, the worse
your near vision. The number can range from J1 to J16. For example:
Visual acuity tests usually take about 5 to 10
The health professional tests your eyes
with different lenses until the lens that corrects your vision the best
(sometimes better than 20/20 or 6/6) is found. The result of a refraction test
determines your prescription eyeglass or contact lens strength.
refraction test takes 5 to 30 minutes (30 minutes if dilating drops are used).
Normally, a person's visual
field forms a rough circle with a natural blind spot. If your vision is normal,
you should be able to see objects clearly throughout the entire visual field
except for the area with the natural blind spot. When you are using both eyes
to see, the blind spots do not interfere with your vision.
have vision loss in certain areas of the visual field if you are not able to
Abnormal results during Amsler grid testing
Gaps in different parts of the visual field may have many
causes, including eye diseases (such as glaucoma and macular degeneration) or
nervous system problems (such as stroke). If results on any of the visual field
tests are abnormal, you will need further tests to determine the cause.
Confrontation tests and Amsler grid tests take just a few minutes. More
thorough visual field testing that uses perimetry and tangent screens can take
more than 45 minutes when both eyes are tested.
People who have normal color
vision are able to distinguish the colored numbers, symbols, or paths from the
background of colored dots.
If you are not able to distinguish
some or all of the colored patterns from the background, you may have a color
vision problem. You may be able to pick out some patterns of colors but not
others, or you may be able to pick out patterns that are different from a
person with normal vision, depending on what type of color vision problem you
This test takes only a few minutes.
Many conditions can change your vision test results.
Your health professional will discuss any significant abnormal results with you
in relation to your symptoms and past health.
Reasons you may not be able to
have the test or why the results may not be helpful include:
Other Works Consulted
Chernecky CC, Berger BJ (2008). Laboratory Tests and Diagnostic Procedures, 5th ed. St. Louis: Saunders.
Fischbach FT, Dunning MB III, eds. (2009). Manual of Laboratory and Diagnostic Tests, 8th ed. Philadelphia: Lippincott Williams and Wilkins.
June 9, 2011
Kathleen Romito, MD - Family Medicine & Christopher J. Rudnisky, MD, MPH, FRCSC - Ophthalmology
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