A visual field test measures how far the eye sees in any direction without moving and how sensitive the vision is in different parts of the visual field. This helps doctors to find certain types of injuries and disease, like glaucoma.
We normally see a wide area of the space in front of us. Without moving our eyes, we see not only what is straight ahead, but some of what is above, below, and off to either side. Most people are familiar with this as "peripheral vision." The entire area that we see is called the visual field.
Vision is usually best right in the middle of the visual field. That is why we turn our eyes toward objects that we want to see better. The farther away from the center of our vision an object is, the less clearly we can see it. When an object moves far enough to the side, it disappears from our vision completely.
A visual field test measures two things:
The visual field test can help the doctor find early signs of diseases like glaucoma that damage vision gradually. Some people with glaucoma do not notice any problems with their vision, but the visual field test shows that peripheral vision is being lost.
A visual field test can also help the doctor find out more about the part of the nervous system that allows us to see. The visual part of the nervous system includes the retina (the "film" in the camera-like eye), the optic nerve (the "wire" that carries images from the retina to the brain), and the brain itself. Problems with any part of this system can change the visual field. There are well-known patterns in the test results that help doctors recognize certain types of injury or disease. By repeating more visual field tests at regular intervals, doctors can also tell whether the patient is getting better or worse.
Sometimes the doctor will want to repeat the visual field test right away to make sure the results are accurate. If the patient is tired, for example, the test results can be unreliable.
Your doctor might also recommend that a visual field test be taken again in a few weeks, a few months, or a year. This might be necessary to make sure that no new problems are detected. When a condition like glaucoma is found, visual field tests are performed regularly to find out how well the treatment is working.
Visual field tests are especially important in the treatment of glaucoma. These tests will tell the doctor if vision is being lost even before the patient notices. That is just one of the reasons why people who have glaucoma need to keep all their appointments with their doctor.
There are several types of visual field tests, but they all have one thing in common: the patient looks straight ahead at one point and signals when an object or a light is seen somewhere off to the side.
If the patient turns the eye to look directly at the object or the light, only the very center of the visual field will be tested. The tester will explain to the patient exactly where to look so that the test is accurate.
The confrontation visual field test measures only the outer edge of the visual field, and it is not very exact.
Computerized instruments are available to perform visual field tests and calculate results. These instruments give more reproducible and accurate results because:
A "normal" visual field test means that the patient can see about as well as anyone else does in the center and around the edges of the visual field.
A test that shows visual field loss means that vision in some areas is not as sensitive as normal. It could be just a little vision lost in a small area, or all vision lost in large areas.
The amount of vision lost and the areas affected are measured by the visual field test. These results are printed out by the instrument as patterns of dots or numbers. The patterns tell the doctor a lot about how the eye and the visual field system are working. This helps your doctor decide whether you have a health problem that needs additional testing to be diagnosed or if treatment is recommended.