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 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.
A refraction test shows your level of refractive error and finds out the right prescription for glasses or contact lenses. 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 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 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
Color vision 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.