Visual Field Test

A visual field test is a common eye exam that measures your entire range of vision, including your central and peripheral (side) vision. It helps identify blind spots or areas of vision loss that you might not notice on your own. This test is crucial for detecting and monitoring various eye conditions and neurological disorders that can affect your sight.

What is Visual Field Test?

A visual field test is an eye examination that maps your entire field of vision, which is everything you can see without moving your eyes. This includes both your sharp, central vision and your broader peripheral (side) vision. The test helps your eye doctor identify any blind spots or areas of vision loss that may indicate an underlying health issue.

Your visual field is the full extent of what you can see at any given moment. This includes the direct line of sight (central vision) and everything around it (peripheral vision). Many eye and brain conditions can cause changes to this field, often starting subtly before you notice them. The visual field test works by presenting a series of lights or targets in different parts of your vision while you focus on a central point. Your responses help create a detailed map of your vision, highlighting any areas where you might not see as well. This map allows your clinician to track changes over time or pinpoint specific patterns of vision loss. There are several types of visual field tests. The most common is automated perimetry, where a computer presents lights and records your responses. Another type, Goldmann perimetry, involves a technician manually moving a target. Both methods aim to accurately assess the boundaries and sensitivity of your vision.

Why it's ordered

A visual field test is often ordered to detect, diagnose, and monitor conditions that can damage the optic nerve or affect the brain's visual pathways. It is particularly important for conditions like glaucoma, a leading cause of irreversible blindness, and can also help identify problems related to stroke, brain tumors, or multiple sclerosis.

One of the primary reasons a visual field test is ordered is to diagnose and monitor glaucoma. Glaucoma is a group of eye conditions that damage the optic nerve, often due to high pressure inside the eye. This damage can lead to permanent vision loss, typically starting with peripheral vision, which you might not notice until it's advanced. Regular visual field tests can detect these subtle changes early, allowing for timely treatment. Beyond glaucoma, the test is vital for assessing neurological conditions. For example, a stroke or a brain tumor can affect the parts of the brain responsible for processing visual information, leading to specific patterns of vision loss. The visual field test can pinpoint these patterns, helping doctors locate the problem area in the brain. Other conditions that may warrant a visual field test include multiple sclerosis, which can affect the optic nerve, and certain medications that can have side effects on vision. By providing objective measurements of your visual field, the test offers crucial information that complements other eye exams and helps your doctor make informed decisions about your care.

How to prepare

Preparing for a visual field test is generally simple and requires no special diet or fasting. You should bring your eyeglasses or contact lenses if you wear them, as the test needs to be performed with your best corrected vision. It's also helpful to ask your doctor any questions you have before the test begins.

Before your visual field test, make sure to bring any corrective lenses you use, such as eyeglasses or contact lenses. The test assesses your vision with the best possible correction, so wearing your usual prescription is important for accurate results. If you wear contact lenses, you can keep them in during the test. There are no dietary restrictions or special preparations needed, such as fasting, before a visual field test. You can eat and drink normally. It's also a good idea to get a good night's sleep beforehand, as being well-rested can help you focus during the test. If you have any concerns or questions about the test, don't hesitate to ask your eye care professional before the procedure starts. Understanding what to expect can help you feel more comfortable and ensure you can follow instructions effectively during the test.

What to expect during

During a visual field test, you will typically sit in front of a bowl-shaped instrument with your chin resting on a support. One eye will be covered while you focus on a central light with the other. Small, dim lights will flash in different areas, and you will press a button each time you see one. The test is painless and usually takes 15 to 45 minutes.

When you arrive for your visual field test, you will be seated comfortably in front of a large, bowl-shaped machine. You will place your chin on a chin rest and your forehead against a support to keep your head steady. Your eye care professional will cover one of your eyes, so only one eye is tested at a time. With your uncovered eye, you will be asked to focus steadily on a central target light inside the bowl. It is very important not to move your eye away from this central light, even when you see other lights flash. Small, dim lights will appear briefly in various parts of the bowl, some very faint. Each time you see a light, you will press a handheld button. The test is designed to find the dimmest light you can see in different areas of your visual field. It is normal to miss some lights, especially the very faint ones or those in your peripheral vision. The test is not painful, though some people might experience mild eye strain or fatigue. The entire process typically takes about 15 to 20 minutes per eye, though it can vary depending on the specific test and your condition.

Understanding your results

Your visual field test results will be presented as a map or graph showing areas of normal vision and any blind spots or areas of reduced sensitivity. Your eye care professional will interpret these findings in the context of your overall eye health, medical history, and other diagnostic tests. The results alone do not provide a diagnosis.

After your visual field test, the machine generates a detailed report, often displayed as a gray-scale map or a numerical printout. Darker areas on the map typically indicate areas where your vision is less sensitive or where you have blind spots. Lighter areas represent normal vision. This map provides a precise picture of your visual field. It is crucial to remember that interpreting these results requires the expertise of a qualified eye care professional. They will analyze the patterns of any vision loss, considering whether they are consistent with conditions like glaucoma, stroke, or other neurological issues. For example, specific patterns of peripheral vision loss are characteristic of glaucoma, while other patterns might suggest a problem in the brain. Your doctor will discuss your results with you, explaining what they mean for your specific situation. They will combine this information with findings from other eye exams, such as optical coherence tomography (OCT) or optic nerve examination, and your overall medical history to form a comprehensive understanding of your eye health and determine the best course of action. The visual field test is one important piece of a larger diagnostic puzzle.

Risks

Visual field tests are very safe and carry minimal risks. Most people experience no side effects. Some individuals might feel mild eye strain or fatigue during or immediately after the test due to the concentration required. These minor effects typically resolve quickly without any intervention.

The visual field test is a non-invasive procedure, meaning it does not involve any contact with your eye beyond perhaps a chin rest. There are no known serious risks associated with undergoing this test. It does not involve radiation, injections, or any physical manipulation of the eye. The most common, albeit mild, side effect reported by some patients is temporary eye strain or fatigue. This can occur because the test requires sustained concentration and steady focus on a central point for an extended period. You might also feel a little tired from the mental effort. Any discomfort from eye strain or fatigue usually subsides shortly after the test is completed. You can resume your normal activities immediately afterward, including driving, unless your doctor has given you specific instructions related to other parts of your eye exam (e.g., if your pupils were dilated for a separate test). If you experience any unusual or persistent symptoms, you should inform your eye care professional.

Frequently asked questions

How long does a visual field test take?

A visual field test typically takes about 15 to 20 minutes per eye, so the total time for both eyes can range from 30 to 45 minutes. The exact duration can vary based on the specific type of test and how quickly you respond.

Is a visual field test painful?

No, a visual field test is not painful. It is a non-invasive test that involves sitting in front of a machine and pressing a button. You might experience mild eye strain or fatigue from concentrating, but there is no physical discomfort to your eyes.

Can I drive after a visual field test?

Yes, you can usually drive immediately after a visual field test. The test itself does not affect your vision or require eye drops that would impair driving. However, if your pupils were dilated for other parts of your eye exam, you might need someone to drive you home.

What if I miss some of the lights during the test?

It is completely normal to miss some of the lights, especially the very dim ones or those in your far peripheral vision. The test is designed to find the limits of your vision, so missing some lights is expected and helps create an accurate map of your visual field.

How often do I need a visual field test?

The frequency of visual field tests depends on your eye health and any existing conditions. If you have glaucoma or another condition affecting your vision, your doctor might recommend tests every 6 to 12 months to monitor for changes. For routine screening, it's less frequent.

What is the difference between central and peripheral vision?

Central vision is the sharp, detailed vision you use for tasks like reading or recognizing faces, focusing directly ahead. Peripheral vision is your side vision, allowing you to see objects outside your direct line of sight. A visual field test assesses both.

Sources

• MedlinePlus — Visual Field Test
• Mayo Clinic — Visual Field Test
• Cochrane Library — Visual Field Test