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. The entire area that we see is called our 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.
The visual field test can help us detect early signs of diseases like glaucoma that damage vision gradually. Many people with glaucoma do not notice any problems with their vision, but the visual field test shows that peripheral vision is being lost.
Any problems with the retina, optic nerve and parts of the brain will manifest as particular patterns of visual loss when test results are examined.