During a visual field acuity test, also called a perimetry test, you will respond to a series of flashing lights while looking straight ahead. Your responses will help the doctor determine whether you have a visual field loss.he lighter the area, the more vision the patient has in that part of the eye. Figure 2. Visual field test of a patient with a meningioma shows vision loss (black areas) in half of the right eye, called hemaniopia.