Visual Field Testing Technique

The visual fields of both eyes overlap; therefore each eye is tested independently. The patient should cover their right eye with their right hand (vice versa when testing the opposite eye). With the examiner seated directly across from the patient, the patient should direct their gaze to the corresponding eye of the examiner. The testing itself can be performed using stationary or moving targets (disk mounted on a stick or examiner's fingers).

The normal visual field reaches 180º in the horizontal plane (160º for monocular vision) and 135º in the vertical plane. A moving target should start outside the usual 180º visual field, then move slowly to a more central position until the patient confirms visualization of the target. To perform stationary testing, the examiner holds up a certain number of fingers peripherally, equidistant between the examiner and the patient. The patient is asked to correctly identify the number of fingers. All four quadrants (upper and lower, temporal and nasal) should be tested. Stationary targets are more precise because they present a finer stimulus to the retina and are less easily identifiable relative to a moving target. In addition, for unknown reasons, colored targets such as red or green discs are more sensitive in detecting deficits when compared to a white test object (cotton disc mounted on a stick).

Visual neglect, a defect in central processing (usually the right parietal lobe), may not be apparent in conventional confrontation testing. This type of testing is performed with both eyes open. The examiner presents stimuli in the right and left visual fields simultaneously. A patient with a right parietal lesion, who exhibits neglect, may be able to accurately identify a visual stimulus when each quadrant is tested independently; however, if the examiner presents a stimulus in the right and left temporal region simultaneously, the patient with neglect will only be able to identify the stimulus in the right temporal field. The image in the left field may appear blurry or may not be visualized at all.

Perimetry is used to measure the peripheral and central visual fields of each eye in a more detailed and sophisticated manner. With the use of perimetry, the visual field is plotted in degrees of arc. Several devices exist to aid in the plotting of the visual field. With all perimetry devices, the testing involves the patient fixing their gaze on a central target, while stimuli, usually flashes of light, are presented throughout the central and peripheral visual fields. The patient is directed to respond verbally or by raising their hand if they see the stimulus.

Two general methods of perimetry exist: static and kinetic. Static perimetry tests individual locations throughout the visual field. First, a dim light is flashed on one area of the visual field. The intensity or size of the light is increased until the patient visualizes it. This is repeated throughout all areas of the visual field until a complete visual profile can be created. Kinetic perimetry differs in that the test stimulus is constant throughout the testing (the light is a fixed size and intensity). The stimulus is presented much like in confrontation testing in the periphery first, and then moved gradually to a more central location until the patient is able to visualize the stimulus. A so-called visual field boundary is then mapped based on this testing.

Visual field testing may prove to be difficult as a simple bedside test in children and obtunded patients. However, techniques exist to help the examiner elucidate the defects. In children, the examiner should stand behind the patient and slowly bring an object, such as a toy or game, around to the front of the child, until it is noticed. In obtunded patients, the examiner should assess the patient's blink response to a visual threat, such as the examiner's finger or any small object that is quickly moved toward the patient's eye in all regions of the visual field. In addition, static perimetry testing has also been shown to be possible at age 5 years, increasing in reliability with age.