Examination of the visual fields helps to localize and identify diseases affecting the visual pathways (▶ Fig. 3.1). Visual field testing is useful when evaluating patients complaining of visual loss (especially when the cause of visual loss is not obvious after ophthalmic examination) or patients with neurologic disorders that may affect the intracranial visual pathways (e.g., pituitary tumors, strokes involving the posterior circulation, and traumatic brain injuries). Fig. 3.1 a-b (a) Lesions of the visual pathways (Adapted Rokhamm R. Color Atlas of Neurology. New York, NY: Thieme; 2004:81). (b) Types of visual field defects secondary to lesions along the visual pathways. Note that the visual pathways (a) are shown with the right eye on the left and the left eye on the right (similar to a computed tomographic or magnetic resonance imaging scan). (continued) (continued) The visual field defects (b) are by convention shown with the right eye on the right and the left eye on the left. Examination allows localization by correlating the shape of defects to the abnormal portion of the visual pathways. It can be repeated to monitor if the defects are growing or shrinking as a measure of whether the disease process is worsening or improving. The visual field and retina have an inverted and reversed relationship. Relative to the point of fixation: The upper visual field falls on the inferior retina (below the fovea). The lower visual field falls on the superior retina (above the fovea). The nasal visual field falls on the temporal retina. The temporal visual field falls on the nasal retina. The nasal fibers of the ipsilateral eye (53% of all fibers) cross in the chiasm to join the uncrossed temporal fibers (47% of all fibers) of the contralateral eye. They form the optic tract, which synapses in the lateral geniculate nucleus to form the optic radiations, which terminate in the visual cortex (area 17) of the occipital lobe. Because more fibers in the optic tract come from the opposite eye (crossed fibers), a relative afferent pupillary defect (RAPD) is often observed in the eye contralateral to an optic tract lesion (see discussion later in this chapter). At the level of the chiasm, the crossing inferonasal fibers travel anteriorly toward the contralateral optic nerve before passing into the optic tract. This is called Wilbrand’s knee and is responsible for the “junctional scotoma” in lesions of the posterior optic nerve. Although the anatomical presence of Wilbrand’s knee is debated, junctional scotomas are observed clinically. The visual field of each eye overlaps centrally. The normal visual field in each eye is approximately (▶ Fig. 3.2) Fig. 3.2 Normal visual fields (Goldmann visual fields). By convention, the visual field of the right eye is placed on the right, and the visual field of the left eye is placed on the left (as if the patient were looking at his or her own visual field). Although the visual field of each eye overlaps, each eye is examined separately and is represented separately. 60 degrees superiorly 70 to 75 degrees inferiorly 60 degrees nasally 100 to 110 degrees temporally The physiologic blind spot corresponds to the optic disc (which has no overlying photoreceptors) and is located approximately 15 degrees temporally in each eye. Current methods of visual field testing all require the subject to indicate whether the stimulus is seen or not. You cannot reliably test the visual field of an uncooperative or very sick patient. There have been attempts to develop an “objective perimetry” by projecting stimuli onto discrete areas of the retina and using electroretinographic or pupillometric responses as end points, but these methods remain experimental. Visual fields should be tested monocularly given that the overlap in binocular fields may mask visual field defects. Bedside visual field testing is quick and easy but has relatively poor reliability, depending on the patient’s ability to identify and describe the visual field defect. Face: Ask the patient to look at your nose and tell you if any parts of your face are missing. Grid: Present a square grid of lines and ask the patient to fixate on a central point and to draw any area in which the lines disappear (▶ Fig. 3.3) Fig. 3.3 a–c (a) Amsler grid testing. (b) Normal Amsler grid (evaluates the central 10 degrees). (c) Amsler grid showing a small central scotoma in one eye. Finger confrontation: This is useful in identifying dense hemianopic or altitudinal defects (▶ Fig. 3.4). Fig. 3.4 a–c Confrontation visual field testing. See text for a description of the technique. The test involves the following steps: Line up the patient across from you. Have the patient cover one eye and stare into the opposite eye on your face with his or her open eye to maintain central fixation. Instruct the patient to count fingers presented within the central 30 degrees (in each of four quadrants around fixation). Special attention should be directed to the horizontal and vertical axes of the visual field to see if there is a change in vision across an axis. The patient should perform the task equally well in all four quadrants. Ask the patient to count fingers in two quadrants simultaneously. If a quadrant of the visual field is consistently ignored, a subtle field defect (or neglect) has been revealed. The far periphery can be assessed by finger wiggle. A consistent difference in color perception (use a red object) across the horizontal or vertical meridian may be the only sign of an altitudinal or hemianopic defect, respectively. The tangent screen is rarely used and is primarily helpful for evaluating patients suspected of nonorganic constriction of the visual field (▶ Fig. 3.5). Fig. 3.5 Tangent screen. See text for a description of the technique. The test involves the following steps: The patient sits 1 m from a black screen (mounted on a wall) on which there are concentric circles. While the patient is asked to fixate on a central target, a white or colored circular stimulus is slowly moved from the periphery toward the center of the screen until the patient reports seeing the stimulus. By repeating this in various parts of the visual field, an isopter can be plotted and then drawn on the screen with chalk or pins. By varying the distance of the patient from the screen, it is possible to differentiate organic from nonorganic constriction of the visual field: in organic patients, the visual field enlarges when the patient is placed farther away from the screen (see Chapter ▶ 18). Goldmann perimetry has the advantage of charting the entire visual field and includes the far temporal periphery (▶ Fig. 3.2, ▶ Fig. 3.3, ▶ Fig. 3.4, ▶ Fig. 3.5, ▶ Fig. 3.6, ▶ Fig. 3.7). It can quickly establish the pattern of visual field loss in the ill, poorly attentive, or elderly patient who requires continued encouragement to maintain fixation and respond appropriately. Fig. 3.6 a–c Goldmann perimetry. See text for a description of the technique. Fig. 3.7 a, b (a) Normal Goldmann visual field test. The right eye is on the right, and the left eye is on the left. Note the normal physiologic blind spot in the temporal field of each eye. (b) Goldmann visual field test showing a left homonymous hemianopia. The test involves the following steps: Place the patient’s head on a chin rest on the open side of a white hemispheric bowl. Cover one of the patient’s eyes. Tell the patient to fixate on a central spot. Present stimuli consisting of dots of white light projected one at a time onto the inner surface of the bowl, usually moving from the unseen periphery into the patient’s field of view. Ask the patient to signal detection of the white dot by pressing a buzzer. Note the responses on a chart representing the visual field. Lights of different sizes and brightness allow the drawing of isopters. The quality of the field is examiner-dependent, and it does not detect subtle changes. Defects are more difficult to quantify than with automated perimetry. Automated perimetry is more sensitive, quantitative, and reproducible, but it is more time consuming and requires good patient cooperation and attention (▶ Fig. 3.8). It is the technique of choice for patients with optic nerve lesions, papilledema, chiasmal compressive lesions, and other progressive visual disorders. Although numerous automated perimetries are available, the Humphrey strategies, in particular, the Swedish Interactive Thresholding Algorithm (SITA) standard and SITA fast programs, are the most commonly used. These tests average about 3 minutes (fast) and 6 minutes (standard) per eye. Fig. 3.8 Automated perimetry. See text for a description of the technique. The test involves the following steps: Place the patient’s head on a chin rest in front of a computer screen. Cover one of the patient’s eyes. Tell the patient to fixate on a central spot. Present stimuli consisting of dots of white light projected one at a time onto the screen, randomly presented (not moving). Ask the patient to signal detection of the white dot by pressing a buzzer. The stimulus size is kept the same, but the brightness varies. Only the central 10, 24, or 30 degrees is usually tested. Humphrey perimetry uses computerized programs to randomly test points in the patient’s central visual field with a standard stimulus size but varying stimulus intensities (▶ Fig. 3.9). It uses a threshold strategy, in which the stimulus intensity varies and is presented multiple times at each location so that the level of detection of the dimmest stimulus is determined. This is then reported on a computerized printout in various ways, some numerical, others pictorial. Fig. 3.9 a–c (a) Normal Humphrey visual field test assessing the central 24 degrees. The right eye is on the right, and the left eye is on the left. Note the normal physiologic blind spot in the temporal field of each eye. (b, c) Humphrey visual field test showing a complete left homonymous hemianopia. (There is a temporal defect in the left eye and a nasal defect in the right eye; both defects respect the vertical meridian. The gray scale (b) and the pattern deviation (c) are shown.)
3.1 Visual Pathways
3.2 Techniques to Evaluate the Visual Field
3.2.1 Visual Field Testing at Bedside
3.2.2 Visual Field Testing in the Office
Tangent Screen
Goldmann (Kinetic) Perimetry
Automated Static Perimetry
3.3 Interpretation of a Visual Field Defect
3.3.1 Understanding a Humphrey Visual Field Printout
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