Results with multichannel topographical bipolar recordings of the visual evoked potential in normals and amblyopes

The method currently used to record topographical voltage distributions of visual evoked potentials is that of monopolar recording with respect to some arbitrary reference electrode. As an alternative we investigated the method of bipolar topographical recording of the checkerboard reversal evoked potential in four amblyopic patients and ten normal persons. The recordings were performed with a system of 14 bipolar channels, arranged in a rectangular grid with an interelectrode distance of 15% of the inion-nasion distance and centered 3 cm above the inion. The gradient distributions of the visual evoked potential obtained from normal persons showed at the time of component P2 a maximum about 3 cm above the inion. The healthy eyes of the amblyopic patients showed similar distributions and latencies. The amblyopic eyes showed normal or reduced amplitudes and normal or increased latencies with large checks and low amplitudes with smaller checks. The topographical distributions recorded with the bipolar recording system showed shifts of the maxima with the larger patterns in three of four amblyopic eyes. A technical comparison showed that these shifts can be recorded by the bipolar recording method with higher accuracy than with the monopolar method, promising a better understanding and more accurate diagnosis of amblyopia.