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 done:
Color vision tests may be done:
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?).
Visual acuity tests are used to evaluate eyesight. Several types of visual acuity tests may be used.
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 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 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.
Using a 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 best.
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 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 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 an allergic reaction.
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.
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.
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).
A 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 minutes.
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.
A 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.
You may have vision loss in certain areas of the visual field if you are not able to see:
Abnormal results during Amsler grid testing include:
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 have.
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.
|Primary Medical Reviewer||Kathleen Romito, MD - Family Medicine|
|Specialist Medical Reviewer||Christopher J. Rudnisky, MD, MPH, FRCSC - Ophthalmology|
|Last Revised||June 9, 2011|
Last Revised: June 9, 2011
Author: Healthwise Staff
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