Visual Field Defects

Andrew G. Lee and Paul W. Brazis

This chapter can be used to localize visual field defects. Figure. 7–1 shows the topographical anatomy of the visual field correlated with the visual pathway. Before using the figure you should establish the following (Table 7–1):

• Is the visual field defect monocular or binocular?

• Monocular visual field defects are due to lesions of the ipsilateral retina or optic nerve, with the exception of the monocular temporal crescent (see below).

• Binocular visual field defects may be due to bilateral retinal or optic nerve disease or may be chiasmal or retrochiasmal lesions.

• Is the visual field defect a monocular temporal crescent?

• If binocular, is it hemianopic or not?

• Is this junctional visual field loss?

• If it is hemianopic, is it bitemporal or homonymous?

• Is this a lateral geniculate or optic tract lesion?

• Are there other localizing signs present?

• If hemianopic, is the field congruous or incongruous?

• Is there macular sparing?

• Is the field defect denser superiorly or inferiorly?

NORMAL VISUAL FIELD IN DEGREES METHODS OF TESTING THE VISUAL FIELDS (FIG. 7–2)

• 50 degrees nasally

• 60 degrees superiorly

• 70 degrees inferiorly

• 80 to 90 degrees temporally

TOPOGRAPHIC ANATOMY OF THE VISUAL FIELD (FIG. 7–1)

• Retinal nerve fiber layer

• Optic nerve axons

• Optic chiasm

• Temporal fibers remain uncrossed in the optic chiasm.

• Nasal fibers cross into the contralateral optic tract in chiasm.

• Inferonasal fibers enter into the contralateral optic nerve for a short course before continuing on to the contralateral optic tract (Wilbrand’s knee). The knee may not exist anatomically (may be an artifact of fixation), but the finding of a junctional scotoma still has localizing value clinically.

• Fibers from the optic tract travel to the lateral geniculate body.

• Inferior fibers pass as optic radiations in the temporal lobe.

• Superior fibers pass in the parietal lobe radiations.

• Radiations reach the occipital lobe (calcarine cortex).

• Anterior portion of the occipital lobe fibers represented monocularly as the temporal crescent.

METHODS OF TESTING THE VISUAL FIELDS

CONFRONTATION TESTING

• Examiner’s hand or fingers presented in four quadrants.

• Examiner’s own visual field serves as the control.

• Colored test objects (red) may enhance sensitivity.

FIGURE 7–1 Schematic diagram of the visual pathways and possible visual field defects.

• Reasonable routine screening test

• Testing of central field with the examiner’s face as the test object

AMSLER GRID

• Useful test of the central 20 degrees at 30 cm

• Especially helpful in macular disease or small central or paracentral scotomas

TANGENT SCREEN

• Tests central 20 to 40 degrees

• Helpful in patients who are unable to be tested by formal perimetry

• Testing available at various distances (e.g., 1 m and 2 m)

• Good test for detecting nonorganic “tunnel” fields (nonorganic field fails to expand appropriately with doubling of the test distance and test object size)

• Various-sized test objects can be used.

• Different colored test objects may enhance sensitivity (red).