What is a visual field test?
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:
- How far up, down, left and right the eye sees without moving.
- How sensitive the vision is in different parts of the visual field.
Why do people need a visual field test?
The visual field test can help Dr. Boyle find early signs of diseases like glaucoma that damage vision gradually. Some people with glaucoma may 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 Dr. Boyle 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 Dr. Boyle recognize certain types of injury or disease. By repeating more visual field tests at regular intervals, we can also tell whether the patient is getting better or worse.