Visual Field Test: What It Is and What the Results Mean

A visual field test is part of a comprehensive eye exam and part of a neurological examination. This non-invasive test examines your fields of vision, and it is important for identifying vision problems that could be signs of eye disease or conditions that affect the brain (like a stroke). If your visual field test is not normal, you may need additional follow-up testing, as well as treatment.

A visual field test can help diagnose scotomas, or blind spots. It can also help identify loss of peripheral or side vision. Loss of side vision is an indicator of glaucoma, a disease that can lead to blindness.

This article describes what to expect during a visual field test, why it's done, and what the results mean.

What Is a Visual Field Test?

Visual field testing is done while your gaze is fixed on a central point directly in front of you to assess what you can see straight ahead, on the sides, and up and down. It can help identify scotomas or "blind spots." These are areas in the field of vision where you are unable to perceive an image.

Four quadrants are used:

• Temporal: toward your ear
• Nasal: toward your nose
• Superior: upper, or above center
• Inferior: lower, or below center

A normal visual field measures about:

• 90 degrees temporally
• 60 degrees nasally and superiorly
• 70 degrees inferiorly

One eye is tested at a time. This is because the visual fields of the eyes overlap. Visual pathways carry information from the eye to the visual part of the brain. There, the information is processed into vision.

Purpose of a Visual Field Test

A visual field test measures how well you can see above, below, and on either side of you. This test can help diagnose diseases of the eye, optic nerve, and central nervous system.

Your vision relies on your retina, optic nerves, and your brain. Vision loss occurs due to diseases that affect any part of this pathway. Certain patterns of visual field loss can help identify the cause of your vision problem and may detect subclinical (not causing symptoms yet) problems.

One eye or both eyes can have a visual field defect:

• Congruity is a visual field defect that is similar in both eyes. Congruity usually means there is a problem affecting the brain, like a stroke. 
• Visual field loss in one eye is usually caused by a condition affecting the eye or the optic nerve, like multiple sclerosis or a tumor affecting the eye.
• Visual field loss in both eyes that is unequal usually means there is a disease process affecting the eyes, like diabetes or glaucoma.

A visual field test typically takes about five to 10 minutes.

Who Should Have a Visual Field Test?

People with certain conditions of the eyes need to be monitored regularly for signs of disease progression and vision loss. You should also request a visual field test if you believe you are having vision problems.

Causes of abnormal visual fields include:

• Glaucoma
• Diabetes
• High blood pressure
• Multiple sclerosis
• Optic glioma
• Hyperthyroidism
• Pituitary gland disorders
• A brain tumor
• A brain aneurysm
• Stroke
• Macular degeneration
• Giant cell arteritis
• Head trauma

People with diabetes and high blood pressure are at increased risk for vision problems. If you have these conditions, your healthcare provider may recommend regular visual field testing to monitor how these conditions are affecting your eyes.

For people with healthy vision, visual field testing is part of a regular comprehensive eye exam. The American Academy of Ophthalmology recommends regular exams at specific intervals based on age.

• Adults with no signs or risk factors for eye problems should have a baseline exam at age 40. If they're found to be healthy, they should have an exam every two to four years until age 54.
• People 55 to 64 should have an eye exam every one to three years.
• Those 65 and over should have one every one to two years.
  

Types of Visual Field Tests

Methods for testing visual field vary. Some simple screening tests can be done in a few minutes during a regular vision check-up. Other tests are more complicated and comprehensive computerized tests.

Confrontation Visual Field Test

During this test, the healthcare provider or technician sits at eye level in front of the patient. Each eye is tested separately as the other eye is covered.

The tester holds up one, two, or three fingers in one of four parts of the visual field. The patient focuses on one of the tester's eyes and tries to determine how many fingers are being held up.

Static Automated Perimetry

During this test, the patient looks directly at a central point within a dome. A machine presents flashing lights of different sizes and brightness in different parts of the visual field. The machine gradually increases the size or brightness of the lights. The patient pushes a button when the lights become visible.

The results of this test aren't always perfect. A patient's eye might wander from the central point, for example, or the patient might accidentally push the button before seeing the light. For that reason, this test is usually repeated two or three times in one session. Because automated visual field testing machines are computerized, the test results can be tracked. The computer can use certain calculations to rule out errors.

Kinetic Perimetry

During this test, the patient looks at a central point. A light is presented in the peripheral vision and is moved toward the central point. The patient pushes a button when the light becomes visible.

This test may be done on a screen or manually. The manual technique is called Goldmann kinetic perimetry.

Kinetic perimetry may be used to find vision problems located in the central nervous system. This includes visual changes caused by a stroke or optic neuritis.

Frequency Doubling Perimetry

During this test, a compact machine presents flickering images in varying intensities. The patient presses a button when the images can be seen. This type of machine is also used to test for glaucoma.

Amsler Grid

The Amsler grid is a simple pattern of squares with a dot in the middle. It is often used to test for central vision field problems.

During this test, the patient focuses on the dot with one eye at a time. If parts of the grid appear distorted, blurry, dark, or blank, it can indicate a visual field deficit. The Amsler grid is often used to test for macular degeneration.

Electroretinography

An electroretinogram is a test that measures the function of the retina. During this test, electrodes attached to the eye or the lower eyelids measure the retina's response to different strength flashes of light.

The test typically includes a 20-minute period of dark adaptation, which helps assess how well you see in low light.

Interpreting the Results of Your Visual Field Test

Test results are often presented in charts. These charts show the range of sensitivity, or how well you can see in different parts of your field of vision.

The charts may include:

• Gray-scale map: Darkened areas in a gray-scale chart show the parts of your visual field that may have vision loss or blurred vision.
• Decibel scale: Test results are measured in decibels (dB). The scale shows a range of sensitivities at different test locations. The range of the scale depends on the type of test. It also depends on the patient's age. It may go from 0 dB, which indicates an inability to see intense light, to up to 32 dB.
• Mean deviation (MD): This is the average difference between the patient's overall visual field sensitivity compared to normal vision in the same age group. The mean deviation value becomes more negative as the overall field vision gets worse. Normal values are typically within 0dB and -2dB. OdB is no different from normal vision. Below -2dB may indicate a problem with vision.
• Total deviation (TD): These charts show all parts of a person's visual field that differ from people who see normally in the same age group. The numbers show the difference between the patient's test results and what is expected for their age. Black squares are more likely to show abnormal vision than lighter gray shading.
• Pattern deviation (PD): This shows more local deviation results and how much the shape of a patient's field differs from normal. Pattern deviation charts can be useful in tracking changes in a glaucoma-related vision problem.
• Visual field index (VFI): This is similar to the mean deviation. It gives a percentage for overall vision. A VFI of 100% indicates perfect vision. 0% means there is no measurable vision.

What Happens After Your Visual Field Test?

If you have abnormal results, your healthcare provider may order additional tests. Depending on your results, you may need to see a specialist, such as a neurologist or an endocrinologist.

The next stages of testing might involve brain imaging or blood tests.

Blood tests screen for conditions like:

• Diabetes
• Hypertension
• Thyroid disease

Imaging tests may include brain imaging, such as a brain MRI. Sometimes visual evoked potentials may be ordered to assess nerve function.

Monitoring Glaucoma

Most types of glaucoma begin with loss of peripheral vision. If you have signs of glaucoma, your healthcare provider will probably order a visual field test. The data will help determine how severe your glaucoma is and how far it has progressed. It also helps your healthcare provider decide if you need any changes to your medication.

Once you've been diagnosed, your eye doctor may want to do a visual field test within three to 12 months. This helps monitor how the disease is progressing. After that, you may need to be tested once or twice a year.

Summary

A visual field test is often done as a part of an annual eye exam. It helps your healthcare provider understand how well you can see above, below, and on either side of you. 

The results of these tests can point to specific types of vision loss. They can also help doctors monitor the progression of glaucoma.

There are a few different types of visual field tests, and they are all non-invasive. 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 other people your age.

Depending on your test results, you may need to be referred to a specialist. Follow-up tests may be ordered. If you have glaucoma, you may need to do visual field testing a couple of times a year. This helps your doctor monitor the progression of your disease.