[Lissajous figures of the visual evoked potentials].

The value of the visual evoked potential (VEP) technique for diagnosis of epilepsy is limited. Except for photosensitive epilepsies, the visual evoked potentials (VEPs) do not reveal more than a routine EEG. As one of the reasons of that, it is pointed out that a review of VEP literature reveals different "normal values" for peak latencies and amplitudes. Thus in this study, lissajous figures of VEPs (VEP-L) were attempted instead of the measurement of peak latencies and amplitudes of VEPs. Thirty six epileptic subjects (14 have partial seizures, 22 have generalized seizures) and 22 control subjects were investigated. Several EEGs to storoboscopic flashes were recorded from scalp electrodes placed at the frontal (Fz) and occipital (Oz) regions according to the 10-20 electrode system, using a right ear as nonreference with a EEG amplifier (Nihon Kohden ME-175 E) and a data recorder (TEAC R-60). Then the phasic relationships between the VEPs from the two areas were analyzed with a medical computer (Nohon Kohden ATAC-2300) and printed out as VEP-L. The results are summerized as follows: First, as time passes from 100 msec to 200 msec in the VEP-L, the epileptic patient group showed more right-roted types than that of the control group (p less than 0.01). Second, the VEP-L at the periods from 50 msec after photic stimulus, were classified into 5 types inspectively. The 5 types are the right-ascending type, the left-ascending type, the vertical type, the horizontal type, and the circular type.(ABSTRACT TRUNCATED AT 250 WORDS)