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. 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.