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    Congruency Rule Questioned in Homonymous Hemianopia

    Localization of brain lesions based on visual field defect congruity may require less rigid paradigm

    THURSDAY, May 31 (HealthDay News) -- The rule of congruency should be used cautiously in patients with homonymous hemianopia, because patients may or may not have occipital lesions or other types of lesions, researchers report in the May issue of the American Journal of Ophthalmology. The occipital lobe is affected in patients with congruent visual field defects, particularly due to stroke, but 50 percent of lesions in other locations also cause congruent defects.

    Valerie Biousse, M.D., of Emory University in Atlanta, and colleagues studied 530 patients with 548 incomplete homonymous hemianopia, including 373 with congruent and 175 with incongruent homonymous hemianopia.

    In congruent versus incongruent homonymous hemianopia, the researchers found that the lesion locations included the occipital lobe in 47.9 percent versus 21.3 percent, the occipital lobe and optic radiations in 8.3 percent versus 5.6 percent, optic radiations in 32.4 percent versus 50.6 percent, the optic tract in 7.2 percent versus 16.3 percent, and other locations in 4.2 percent versus 6.3 percent.

    "When faced with a patient demonstrating a congruous homonymous hemianopia, this study confirms that the most likely cause is an occipital lesion and, in the absence of other neurologic abnormalities, that it represents an infarction," states the author of an accompanying editorial. "But it makes a valuable new point: our degree of confidence should be substantially less than prior teaching suggests. The patient with this pattern should not be presumed to have experienced a relatively benign, isolated ischemic event; neuroradiologic investigation into the cause and the location of the damage is essential."

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