Test Overview

Vision tests check many different functions of
the eye. Some of 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. Others may check how sensitive you are to glare (brightness acuity), how well your eyes work together to provide depth perception, and more.

Vision tests are usually done along with exams and tests that check the health of the eye. Here are some common tests that check for blurred or low vision.

  • Visual acuity (sharpness) tests. These tests help your doctor find out if you have a problem that affects how well you can see. They measure the eye’s ability
    to see details at near and far distances. The tests usually involve reading
    letters or looking at symbols of different sizes on an eye chart. Usually, each
    eye is tested by itself. And then both eyes may be tested together, with and
    without corrective lenses (if you wear them). Several types of visual acuity
    tests may be used.
  • Refraction test. This test shows your level of refractive error and finds out the right prescription for glasses or contact lenses. Refractive errors, such as
    nearsightedness or
    farsightedness, occur when light rays entering the eye
    can’t focus exactly on the nerve layer (retina) at the
    back of the eye. This causes blurred vision. Refraction is done as a routine
    part of an eye exam for people who already wear glasses or contact
    lenses. But it will also be done if the results of the other visual acuity
    tests show that your eyesight is below normal and can be corrected by glasses.
  • Visual field tests. They are used to check for
    gaps in your side (peripheral) vision. Your complete visual field is the entire
    area seen when your gaze is fixed in one direction. The complete visual field
    is seen by both eyes at the same time. It includes the central visual
    field-which detects the highest degree of detail-and the peripheral visual
    fields.
  • Color vision tests. These tests check your
    ability to distinguish colors. They are used to screen for
    color blindness in people with suspected retinal or
    optic nerve disease or who have a
    family history of color blindness. Color vision
    tests are also used to screen applicants for jobs in fields where color
    perception is essential, such as law enforcement, the military, or electronics.
    Color vision tests only detect a problem-further testing is needed to identify
    what is causing the problem.

Why It Is Done

Visual acuity tests

These tests may be done:

  • As part of a routine eye exam to screen for
    vision problems. How often you should have routine eye exams changes as you
    age. Adults and children and teens have different schedules for eye exams.
  • To monitor an eye problem, such as
    diabetic retinopathy, or to find out if a treatment is working.
  • To determine if you
    need glasses or
    contact lenses to improve your
    vision.
  • After an injury to the eye, to check if your sight was affected.
  • When you obtain or
    renew your driver’s license or for some types of employment.
  • To check the near vision of school-age children who have trouble reading, poor school performance, or blurred vision while doing work up close.

Refraction

This test is done:

  • To determine the correct prescription for
    eyeglasses or contact lenses.
  • To find out if blurred vision is caused by refractive error or eye disease.

Visual field tests

These may be
done:

  • To check for vision loss in any area of your
    visual field.
  • To screen for eye diseases, such as
    macular degeneration and
    glaucoma, which cause gaps in the visual
    field.
  • 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

These tests may be
done:

  • As part of a routine eye
    exam.
  • To screen for or diagnose color
    blindness.
  • To screen applicants for jobs in which color perception
    is important, such as truck driving, electronics, or the military.

How To Prepare

If you wear glasses or contact lenses, bring them
with you to the exam since the tests cannot be properly performed
without them. If you have a copy of your current eyeglass prescription, bring
it with you.

If you have a young child, it is best to practice eye tests at home before you take your child to the appointment. This can help your child cooperate better during the real testing. For more information, see the topic Pediatric Preparation for Medical Tests.

Many medicines may affect the results of vision
tests. Be sure to tell your doctor about all the over-the-counter
and prescription medicines you take.

Talk to your doctor 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

Visual acuity
tests are used to evaluate eyesight. Several types of visual acuity tests may
be used.

  • 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
      wearing them.
    • Let your doctor 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).

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
assistant, an
ophthalmologist, an
optometrist, a teacher, or some other trained person.
Testing may be done at a doctor’s office, school, workplace, health fair, or
elsewhere.

Refraction

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
corrective lenses.

Your doctor 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.

The doctor may put a device (called a phoropter) in front of your eyes. The device contains many different lenses. Testing one eye at a time, the
doctor 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 doctor will continue to test your eyes with
different lenses until it is determined which lenses correct your vision the
best. Your doctor may use a hand-held device (retinoscope) to 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.

Visual field tests

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.

  • The confrontation test. Your doctor sits or stands
    2 ft (0.6 m) to
    3 ft (1 m) in front of you. You
    cover one eye while fixing your gaze on his or her nose. He or she slowly moves
    a finger or hand from the outer edge of your visual field toward the center and
    from the center toward the edge through all areas of your visual field. You
    will focus your eye on your doctor’s nose and signal when you first see his or
    her finger or hand. The test is then repeated for the other eye.
  • The Amsler grid test checks for
    macular degeneration, a disease that causes loss of
    vision in the center of your visual field. The test uses a
    4 in. (10 cm) square chart with
    straight lines that form boxes. The grid has a black dot at the center. The
    chart is held about
    14 in. (36 cm) from your face.
    You cover one eye while focusing your other eye on the black dot. The test
    is then repeated on the other eye. Tell your doctor if:

    • You cannot see the black
      dot.
    • You see a blank or dark spot (other than the center
      dot).
    • The lines in the grid look wavy, blurred, or curved instead
      of straight. You will be asked to point to the specific abnormal area of the
      grid.
  • Perimetry testing uses a
    machine that flashes lights randomly at various points in the visual field. You
    look inside a bowl-shaped instrument called a perimeter. While you stare at the
    center, lights will flash, and you press a button each time you see a flash. A
    computer records the location of each flash and whether you pressed the button
    when the light flashed in that location. At the end of the test, a printout
    shows any areas of your visual field where you did not see the flashes of
    light. In an alternative manual perimetry test, your doctor moves
    a light target and notes your visual field on paper.
  • The
    tangent screen test uses a black screen with concentric
    circles and lines leading out from a center point (like a bull’s-eye). Sitting
    3 ft (1 m) to
    6 ft (2 m) away from the
    screen, you cover one eye while fixing your gaze on a target point marked on
    the screen. Test objects of various sizes at the tip of a wand are then moved
    inward from the outer edge of the screen toward the center. You will signal
    when you can see the object, and that point is then marked on the screen. The
    points on the screen where you see the objects are connected to provide an
    outline of your visual field. The test is then repeated for the other eye. An
    alternative manual tangent screen test uses a white object against a black
    background. If you wear glasses, you will keep them on for this test.

Color vision tests

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
colored dots.

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 doctor holds the color test patterns about
14 in. (36 cm) away from you.
Some patterns are harder to pick out than others. As the doctor 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.

How It Feels

You should not feel any discomfort
during these vision tests.

When dilating eyedrops are used

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, unless your doctor says it is okay. Wearing sunglasses may make you more comfortable until the effect of
the drops wears off.

Risks

In some people, the dilating eyedrops can cause
an
allergic reaction.

Results

Vision tests check many different
functions of the eye. Your doctor will let you know if your eyesight is normal or if it is better or worse than normal. He or she may also be able to tell you why you have a vision problem.

Visual acuity testing

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.

20/20
(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.

  • When the second number is smaller than the
    first number, the person’s vision is better than normal. For instance, a person
    with 20/10 (6/3) vision can see from
    20 ft (6 m) what people with
    normal vision can see from
    10 ft (3 m).
  • When
    the second number is larger than the first number, the person’s distance vision
    is worse than normal.
  • A person with 20/200 (6/60) vision or less
    in his or her best eye when wearing corrective lenses is considered legally
    blind.

Your doctor will also tell you if you have reduced near vision.

Refraction

The doctor 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.

Visual field test

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.

You may
have vision loss in certain areas of the visual field if you are not able to
see:

  • Test objects during tangent screen
    testing.
  • Movements or light flashes during perimetry
    testing.

Abnormal results during Amsler grid testing
include:

  • Not being able to see the black dot at the
    center of the grid.
  • Not being able to see all four edges of the
    grid.
  • Having blank spots or dark spots on the grid (other than the
    black dot at the center).
  • Seeing lines that look wavy or
    curved.

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.

Color vision test

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
have.

Many conditions can change your vision test results.
Your doctor will discuss any significant abnormal results with you
in relation to your symptoms and past health.

What Affects the Test

Reasons you may not be able to
have the test or why the results may not be helpful include:

  • Your ability to understand or follow
    instructions. Some vision tests cannot be done on babies, small children, or
    people who cannot understand or follow the instructions.
  • Your
    ability to stay alert and respond to questions.
  • Failure to wear
    prescribed eyeglasses or contact lenses.
  • Poor lighting.

What To Think About

  • A complete eye and vision evaluation also
    includes a physical exam of the structures inside the eye. To learn more, see the topic
    Ophthalmoscopy.
  • A test to screen for
    increased intraocular pressure (IOP), which increases your risk for
    glaucoma, is often part of a routine eye exam. It also
    is used to monitor treatment for glaucoma. Tonometry can be used to determine
    whether a medicine is keeping your IOP below a set target pressure determined
    by your doctor. To learn more, see the topic
    Tonometry.
  • Home tests for near vision in
    adults and distance vision in children are available. These tests should not
    replace a thorough eye exam by a doctor.
  • Until your child’s visual system has fully developed, the doctor may check your child’s visual behavior. This includes testing eye movements, the alignment of the eyes, how well your child can track an object, whether your child has depth perception, and how well the two eyes work together. If you notice signs of eye problems in your child, talk to your child’s doctor. To help you decide if you need to see a doctor for a vision problem, see the topic Eye Problems, Noninjury.

References

Other Works Consulted

  • American Academy of Ophthalmology (2012). Refractive Errors and Refractive Surgery (Preferred Practice Pattern). San Francisco: American Academy of Ophthalmology. Also available online: https://one.aao.org/CE/PracticeGuidelines/PPP_Content.aspx?cid=0bc8c7ce-26df-46da-bf2b-7e908bedaf64.
  • Chang DF (2011). Ophthalmologic examinations. In P Riordan-Eva, ET Cunningham, eds., Vaughan and Asbury’s General Ophthalmology, 18th ed., pp. 27-57. New York: McGraw-Hill.
  • Chernecky CC, Berger BJ (2013). Laboratory Tests and Diagnostic Procedures, 6th ed. St. Louis: Saunders.
  • Fischbach FT, Dunning MB III, eds. (2009). Manual of Laboratory and Diagnostic Tests, 8th ed. Philadelphia: Lippincott Williams and Wilkins.

Credits

ByHealthwise Staff
Primary Medical Reviewer Kathleen Romito, MD – Family Medicine
Adam Husney, MD – Family Medicine
Specialist Medical Reviewer E. Gregory Thompson, MD – Internal Medicine

Current as ofMay 17, 2017