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 are
the most common tests used to evaluate eyesight. 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 is a test
that measures the eyes' need for corrective lenses (refractive error). It is
usually done after a visual acuity test. Refractive errors, such as
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 examination 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 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, and it includes the central visual
field-which detects the highest degree of detail-and the peripheral visual
Color vision tests check your
ability to distinguish colors. It is used to screen for
color blindness in people with suspected retinal or
optic nerve disease or who have a
family history of color blindness. The color vision
test is 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 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. For more information, see: