Visual Fields
Testing visual fields is an integral part of the neuro-ophthalmologic examination in any patient with an afferent system problem. In fact, any patient who has decreased vision that cannot be explained on an ocular or refractive basis should have a visual field test.
PRINCIPLES THAT CONTRIBUTE TO VISUAL FIELD INTERPRETATION
Extent of the Normal Monocular Visual Field
• Nasally 60 degrees
• Superiorly 60 degrees
• Inferiorly 70 to 75 degrees
• Temporally 100 to 110 degrees
Retinal Nerve Fiber Anatomy
The basis of visual field defects is the anatomic structure of the retinal nerve fibers. The visual field and retina have an inverted and reverse relationship. Relative to fixation, the inferior visual field falls on the superior retina. The superior visual field falls on the inferior retina, the temporal visual field on the nasal retina, and the nasal visual field on the temporal retina.
Lesions of the optic nerve produce specific patterns of visual field defects within the central 30 degrees of the visual field because retinal nerve fibers enter the optic disc in a specific pattern.
• Arcuate nerve fiber bundles: The superior and inferior nerve fibers are formed into arcuate bundles that course around the papillomacular bundle to enter the optic nerve superiorly and inferiorly, respectively. Peripherally in the retina, they join at a structure called the horizontal raphé. Fibers do not cross this raphé. The nasal most extent of a superior or inferior arcuate defect is the horizontal meridian (Fig. 2-1).
• Papillomacular bundle: Retinal nerve fibers from the macula enter the optic disc temporally. Involvement of the papillomacular bundle produces a central (Fig. 2-2A) or a cecocentral (Fig. 2-2B) scotoma.
• Nasal nerve fiber bundles: These enter the nasal aspect of the optic disc and travel in a straight (nonarcuate) course. The resulting
defect is a wedge-shaped temporal scotoma arising from the blind spot and does not necessarily respect the temporal horizontal meridian.
defect is a wedge-shaped temporal scotoma arising from the blind spot and does not necessarily respect the temporal horizontal meridian.
Lesions of the optic disc will produce visual field defects identical to those of the retina. As the retinal fibers extend posteriorly through the optic nerve toward the chiasm, they rotate 90 degrees, and the macular fibers come to occupy the central core of the optic nerve. Therefore, lesions in the retrobulbar prechiasmal optic nerve tend to produce more central scotomas, while lesions of the intracranial prechiasmal optic nerve may even present a visual field defect that begins to respect the vertical meridian (see Chapter 5).
Testing Strategies
A variety of testing strategies are available to explore the extent of the visual field. The specific technology used is less important than the goal that the method employed arrives at the correct answer as to the form and extent of any scotoma.
Discussion of the types of visual field examinations performed routinely in neuro-ophthalmologic practice follows.
Confrontation Visual Fields
Confrontation fields should be performed on all patients, even those without afferent complaints. Confrontation visual field tests provide a rapid and practical method of visual field assessment that can be performed with minimal equipment and may be the only method of testing readily available. The test is quickly performed and easily understood by most patients. It will identify gross scotomas and has only moderate sensitivity and specificity for identifying small or subtle scotomas. A normal confrontation visual field test does not preclude the need for more automated visual field testing.
Several techniques have been described for performing confrontation visual fields. We describe a few options below. For all tests of confrontation visual fields it is important for the examiner and patient to be seated face to face at a distance of approximately 2 to 3 feet from each other and the patient asked to occlude one eye using either the palm of his or her hand, a patch or other occluding device. The patient is asked to fixate on the examiner’s opposite eye (if the patient’s right eye is being examined, the patient fixates at the examiner’s left eye) or nose.
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