Multifocal Magnetoencephalogram Applied to Objective Visual Field Analysis

Purpose To establish an objective visual field analysis by visual evoked magnetic fields. Methods Forty-eight focal areas of the visual field were stimulated by the visual evoked response imaging system (VERIS). The multifocal visual evoked magnetic fields (mfVEFs) of 11 healthy subjects were recorded. The output signals were recorded with VERIS, and the second-order kernel was calculated. The equivalent current dipoles (ECDs) were estimated, and the relative positioning of ECDs was determined by a magnetoencephalography (MEG) system. Results The mfVEFs consisted of either two- or three-peak waves. Large amplitude mfVEFs were elicited when the stimulus was confined to 6° of the central visual field, but a strong response could not always be obtained between 6° and 12°. All ECDs were estimated to originate in the occipital striate cortex. The ECDs for the upper (lower) field stimulations were estimated to be on the lower (upper) cortex, while those for right (left) field stimulations were on the left (right) cortex. Conclusions The locations of mfVEF peak ECDs were correlated with the stimulated visual field and generally matched the cruciform model. In combination with the multifocal technique, MEG can be used for objective visual field analysis. Jpn J Ophthalmol 2004;48:115–122 © Japanese Ophthalmological Society 2004