Vision Tests

Vision Tests

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:
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

How It Is Done?
Visual acuity tests are used to evaluate eyesight. Several types of visual acuity tests may be used.

The Snellen testchecks 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.

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.