It should be emphasized that movement of the visual target provides the coarsest stimulus to the retina, so that a perception of its motion may be preserved while a stationary target of the same size may not be seen. In other words, moving targets are less useful than static ones in confrontational testing of visual fields. Finger counting and comparison of color intensity of a red object or the clarity of the examiner’s hand from quadrant to quadrant are simple confrontation tests that will disclose most field defects. Glaser recommends presenting the examiner’s hands simultaneously, one on each side of the vertical meridian; the hand in the hemianopic field appears blurred or darker than the other. Similarly, a scotoma may be defined by asking the patient to report changes in color or brightness of a red test object as it is moved toward or away from the point of fixation. A central scotoma may be identified by having the patient fix with one eye on the examiner’s nose, on which the examiner places the index finger of one hand or a white-headed pin and has the patient compare it for brightness, clarity, and color with a finger or pin held in the periphery. In young children or uncooperative patients, the integrity of the fields may be roughly estimated by observing whether the patient is attracted to objects in the peripheral field or blinks in response to sudden threatening gestures in half of the visual field.
We continue to teach that these confrontation techniques are reasonably sensitive for routine clinical work if performed carefully, but we are mindful of the study from Pandit and colleagues, who found false-negative findings in 42 percent of patients tested with quadrant finger counting, using static automated perimetry as a standard. If any defect is found or suspected from confrontation testing, the fields should be charted and scotomas outlined on a tangent screen or perimeter. Although most automated perimetry techniques encompass only the central visual field, this method is usually adequate to detect most clinically important changes.
The method of testing by double simultaneous stimulation may elicit defects in the central processing of vision that are undetected by conventional perimetry. Movement of one finger in all parts of each temporal field may disclose no abnormality, but if movement is simultaneous in analogous parts of both temporal fields, the patient with hemispatial neglect from a parietal lobe lesion, especially on the right, may perceive only the one in the normal right hemifield.
A type of abnormality disclosed by visual field examination is concentric constriction. This may be a result of severe papilledema, in which case it is usually accompanied by an enlargement of the blind spot. A progressive constriction of the visual fields, at first unilateral and later bilateral, associated with pallor of the optic discs (optic atrophy), should suggest a chronic meningeal process involving the optic nerves (syphilis, cryptococcosis, sarcoidosis, lymphoma). Long-standing, untreated glaucoma and retinitis pigmentosa are other causes of concentric constriction. Marked constriction of the visual fields of unvarying degree, regardless of the distance at which the visual field is tested, is termed “tubular constriction”; it defies geometric principles and is a sign of hysteria. With organic disease, the constricted visual field enlarges as the distance between the patient and the testing screen increases.
It is hardly possible within the confines of this chapter to describe all the causes of opacification of the refractive media. Those with the most important medical or neurologic implications are briefly commented upon. Although changes in the refractive media do not involve neural tissue primarily, certain ones assume importance because they are associated with neurologic disease.