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M. Takimoto, K. Yanashima, K. Magatani; Quadrantic Checkerboard Pattern Reversal VEFs: Cases of Visual Field Defect . Invest. Ophthalmol. Vis. Sci. 2004;45(13):254.
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Purpose: We have shown that visual evoked magnetic fields (VEFs) can be obtained from all quadrants of the visual field simultaneously with a quadrantic checkerboard pattern reversal stimulus. It was relatively easy with this stimulus to determine the relative position and strength of the equivalent current dipoles (ECDs) for the four quadrants simultaneously. The purpose of this study was to determine the effectiveness of this stimulus in detecting and evaluating visual field defects. Methods: VEFs were recorded with the whole–head MEG system (Neuromag) from eight normal subjects without any ocular diseases except refractive errors, and from two patients with visual field defects caused by infarction or bleeding in the occipital lobe. Refractive errors were corrected with nonmagnetic lenses in a nonmagnetic frame. The checkerboard pattern reversal stimulus was composed of four quadrants, and each was driven by a different stimulus trigger and interval. VEFs were elicited by stimulating the four quadrants simultaneously. The responses around 100 ms after the stimulus trigger (M100) were estimated. Results: In controls, the M100 responses were recorded from the primary visual cortex during the stimulation of each quadrant. In patients with visual field defects, the M100 responses absent from the quadrant corresponding to the visual field defect, and the M100’s ECD were larger than that of the normal controls. Conclusions: These results indicate that the relative location and strength of the ECDs could be recorded simultaneously for each quadrant, and that this type of stimulation can be used to detect visual field defects objectively in a relatively short period. In addition, they suggest that larger responses in the patients might be in compensation for the visual field defect.
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