Interocular interaction assessed by VEPs to pattern-onset, -reversal, and -offset in normally sighted and amblyopic...

The extent of interocular interaction reflected in sequentially averaged VEPs to checkerboard onset, reversal and offset stimulation was investigated to assess the relative efficacy of the three modes of pattern stimulation. Thirty-one controls and 18 amblyopic children were studied. Components on the side of the scalp ipsilateral and contralateral to the stimulated left half-field were measured for checksizes 12', 20', 50' and 80'. Binocular:monocular amplitude ratios for normals were compared with 'binocular:good eye' amplitude ratios for amblyopes. The reversal P100 ratio was found to differ significantly between normals and amblyopes for 12', 20' and 50' checks. Ipsilateral (CII) and contralateral (P105) onset components also differed significantly but for the smallest 12' checks only. In controls, onset components (P105 and CIII) and, reversal components (N80 and P100) showed significantly shorter binocular as compared with monocular latencies. These latency differences were not found in amblyopes. Our results show that interocular interaction in normals is best shown by potentials which predominantly reflect macular pathway activation, and are most conspicuous for reversal N80 and P100 components. Similarly, these components demonstrated the clearest differences when comparing binocular interaction effects between controls and amblyopic subjects.