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Detection of a Visual Field Defect Caused by Lesion of the Visual Pathway by means of Functional Magnetic Resonance Imaging
1Spang K., 2Hildebrandt H., 3Diehl V., 3Terwey B., 1Fahle M.,
Small structural defects of the visual nervous system may not be detected by objective clinical methods but nevertheless cause extensive defects in the visual field. We examined the possibilities to detect such defects by means of functional magnetic resonance imaging (fMRI), since at present; this method seems to offer the best way to discriminate between organic and functional causes of visual field defects especially of the periphery. FMRI measures changes in local cerebral O2 concentration in the central nervous system (CNS) and hence detects parts of the visual cortex that fail to increase their activity during visual stimulation. By means of this method, we tested a patient suffering from a circumscribed lesion of the left lateral geniculate nucleus, causing a large defect in the right visual field. The fMRI results demonstrated a significant difference between visual stimulation of the left versus right half of the visual field. While a stimulus presentation in the left half of the visual field yielded a strong increase of cerebral blood oxygenation level in the right cortical hemisphere, the reaction to stimulus presentation in the left visual field was far less pronounced in the right hemisphere. The results clearly demonstrate that functional magnetic resonance imaging can detect certain functional defects of vision.