Spatial and temporal properties of interocular timing differences in multifocal visual evoked potentials

The multifocal VEPs (mfVEPs) obtained from the right and left eyes are practically identical in shape and amplitude, however small differences in the implicit times (ITs) have been reported. We have analyzed the ITs in detail to show that they are dependent on the radial location of the stimulus in the visual field. The differences are large, up to 8.3 ms, near the horizontal meridian, and are probably due to differences in the distances of the nasal and temporal ganglion cell axons from the optic disc. The intraretinal conduction velocity of ganglion cell axons, determined by dividing the axonal length to the optic disc by the ITs, was 0.29 m/s at an eccentricity of 0.5-1.4° and 1.39 m/s at 8-12°.