A visual field test measures your entire field of vision. Here is the range you can see:
- the following
- on both sides of you
The test is done with your gaze fixed on a central point directly in front of you.
This test can help find dark spot, or blind spot. It can also help identify loss of peripheral or side vision. Loss of lateral vision is an indicator of glaucoma, a disease that can lead to blindness.
There are several types of visual field tests. The easiest is as a standard part of an annual eye exam.
Depending on the results, your eye doctor may have you repeat the test. You may also need to take additional tests. Frequent visual field tests are often performed to monitor the progression of glaucoma.
This article looks at visual field tests, how they are performed, and how the results are interpreted.
Annual visual field tests are usually covered by vision insurance. For those diagnosed with glaucoma, insurance may cover at least two exams per year. If you do not have insurance, discuss the cost with your doctor in advance.
What is a visual field test?
Your field of view is measured in degrees. Use four quadrants:
- Time: close to your ear
- Nose: towards your nose
- Above: Above, or above the center
- Bottom: below or below the center
Normal visual field measurements are approximately:
- 90 degrees temporarily
- 50 degrees on the nose
- 60 degrees down
Test one eye at a time. This is because the fields of view of each eye overlap. The visual pathway transmits information from the eyes to the visual part of the brain. There, information is processed into visuals.
Different parts of the nervous system and brain control different parts of the visual field. The visual pathway includes everything from the retina to the optic nerve to the cerebral cortex. Different patterns of vision loss have been found in diseases affecting different parts of the vision pathway, such as:
- eye disease
- optic nerve disease
- central nervous system disease
Certain patterns of vision loss may point to potentially problematic areas. E.g, consistency Occurs when visual field defects are similar in both eyes. Increased coherence usually means a problem in the higher cortical parts of the brain.
Loss of function in the lower visual field may point to problems elsewhere. This is usually associated with fibers in the upper retina or nerve head.
Abnormal test results may indicate a problem with your central nervous system, or an undiagnosed health problem. It can also detect:
- Central or peripheral retinal disease
- some eyelid conditions, including sagging or drooping eyelids
- optic nerve disease
- Disorders that affect visual pathways in the brain
Reasons for abnormal perimetry results include:
- multiple sclerosis
- optic glioma
- Pituitary disease
- Central nervous system problems, such as a tumor pressing on a visual part of the brain
- macular degeneration
- giant cell arteritis
A visual field test measures your visual field above, below, and to the sides. This test can help diagnose diseases of the eye, optic nerve, and central nervous system.
Types of Visual Field Tests
Methods for testing visual fields vary. Some simple screening tests can be done in minutes during a routine vision exam. Other tests are more complex and comprehensive computerized tests.
Adversarial visual field test
During this test, the healthcare provider or technician sits in front of the patient at eye level. The patient covers one eye. The tester held up one, two or three fingers in one of the four parts of the field of view. The patient focuses on one eye of the tester and tries to determine how many fingers are lifted. Both eyes were tested separately.
What you should know about the Adversarial Vision Test
Static automatic perimetry
During this test, the patient gazes directly at the center point within the dome. A machine presents flashes of different sizes and brightness in different parts of the field of view. The machine gradually increases the size or brightness of the light. When the light becomes visible, the patient presses the button.
The results of this test are not always perfect. For example, a patient’s eyes may be off-center, or a patient may accidentally press a button before seeing the light. For this reason, this test is usually repeated two to three times in a session. Since the automatic visual field test machine is computerized, the test results can be tracked. Computers can use certain calculations to troubleshoot errors.
During this test, the patient gazes at the center point. Light appears in peripheral vision and moves towards the central point. When the light becomes visible, the patient presses the button.
This test can be done on-screen or manually. The manual technique is called Goldmann dynamic perimetry.
Kinetic perimetry can be used to detect vision problems located in the central nervous system. This includes changes in vision caused by stroke or optic neuritis.
Frequency doubling field of view
In this test, a compact machine presented flicker images of varying intensities. When the image can be seen, the patient presses the button. This machine is also used to test for glaucoma.
The Amsler grid is a simple square pattern with a dot in the middle. It is often used to test for central vision problems.
During this test, the patient focuses on the point with only one eye at a time. If parts of the mesh are distorted, blurred, dark, or blank, it may indicate a lack of visibility. Amsler grids are commonly used to test for macular degeneration.
Testing for Macular Degeneration Using the Amsler Grid
There are several different types of visual field tests. Some are done manually, some are computerized.
Interpreting the results of the visual field test
Test results are usually presented in the form of graphs. These graphs show the sensitivity range, or how well you can see in different parts of the field of view. Charts may include:
- Grayscale image: Dark areas in a grayscale image show areas of your field of vision that may have vision loss or blurred vision.
- Decibel Scale: Test results in decibels (dB). The scale shows a range of sensitivities for different test locations. The scale of the scale depends on the type of test. It also depends on the age of the patient. It can range from 0 dB (meaning no bright light can be seen) to as high as 32 dB.
- Mean Deviation (MD): This is the average difference in a patient’s overall visual field sensitivity compared to someone with “normal” vision in the same age group. As the overall field of view worsens, the mean deviation value becomes more negative. Normal values are usually between 0dB and -2dB. OdB is indistinguishable from normal vision. Below -2dB may indicate vision problems.
- Total Deviation (TD): These graphs show all the parts of a person’s visual field that differ from normal people of the same age group. The numbers show the difference between a patient’s test results and their age expectations. Black squares are more likely to show abnormal vision than light gray shades.
- Pattern Deviation (PD): This shows more local deviation results and how much the shape of the patient’s field of view differs from normal. Pattern deviation charts can be used to track changes in glaucoma-related vision problems.
- Visual Field Index (VFI): This is similar to the mean deviation. It gives a percentage of overall vision. 100% VFI means perfect vision. 0% means no measurable visual acuity.
Visual field test results are usually presented in the form of a graph. These charts give healthcare providers detailed information about where your vision loss is and how your vision compares to others your age.
What happens after a visual field test?
If your results are abnormal, your healthcare provider may order additional testing. You may also be referred to your primary care healthcare provider. Depending on your results, you may need to see a specialist, such as a neurologist or endocrinologist.
The next stage of testing may involve brain imaging or blood tests. Blood tests to screen for the following:
Monitoring for glaucoma
Most types of glaucoma begin with peripheral vision loss. Visual field testing is often used to:
- Diagnosing glaucoma
- Determine the severity of the condition
- monitor its progress
If glaucoma is suspected, your healthcare provider may order a visual field test. These data will help determine the severity and progression of glaucoma.
After diagnosis, you may have visual field tests two or more times a year. This may seem repetitive, but it can help your healthcare provider understand how the disease is progressing. It can also help your healthcare provider decide if you need to make any changes to your medicines.
What should I know about glaucoma?
Based on your test results, your eye care provider may refer you to your primary care doctor or specialist. You may need follow-up tests or long-term monitoring.
Visual field testing is usually done as part of an annual eye exam. It can help your healthcare provider understand your vision above, below, and to the sides.
The results of these tests can indicate a specific type of vision loss. They can also help doctors monitor the progression of glaucoma.
There are several different types of visual field tests. Some are done manually; others are computerized. The results of these tests can help your healthcare provider understand where your vision loss is and how it compares to others your age.
Depending on your test results, you may need a referral to a specialist. Follow-up tests can be ordered. If you have glaucoma, you may need visual field tests several times a year. This helps your doctor monitor your disease progression.
Frequently Asked Questions
How long does the visual field test take?
About five to ten minutes.
If my eyes are healthy, how often do I need to have a visual field test?
Visual field testing is part of a routine comprehensive eye exam. The American Academy of Ophthalmology recommends regular checkups at specific intervals based on age. Adults with no signs of eye problems or risk factors should have a baseline examination at age 40. If they are found healthy, they should be checked every two to four years until age 54. People aged 55 to 64 should have eye exams every one to three years. Those 65 and older should have one every one to two years.
If I have glaucoma, how often should I have a visual field test?
Once you are diagnosed, your eye doctor may want to perform a visual field test within 3 to 12 months. This helps monitor the progression of the disease. After that, you may need to be tested once or twice a year.