MODEL RELEASED. Visual field test. Elderly patient undergoing a visual field test. She is looking into a field analyser machine. An ophthalmologist is watching a monitor on the side of the machine. Field analysers measure the patient's visual field by projecting small spots of light in different positions in front of the eye. When looking straight ahead, the normal human field of vision extends to about 90 degrees out from the midline of the face. This can be reduced by stroke or glaucoma, sometimes without the patient realising it. Stroke victims can lose up to half their field of vision, resulting in a condition called hemianopia.