Binocular cortical interactions in the monofixation syndrome.

This study examines the relationship between clinically assessed binocular sensory status and binocular visual evoked potentials (BVEPs) in 11 patients with monofixation syndrome (MFS) and in 12 patients with absent binocular fusion (ABF). BVEPs were elicited using a two-sinusoid "beat" technique. The luminances of red/green anaglyphic circular fields were modulated independently at temporal rates of 6 and 8 Hz. This stimulus elicits a BVEP at 14 Hz in children with normal stereoscopic vision. In this study, we found that this BVEP also is present in patients with MFS, whereas it is near background noise levels in patients with ABF. These results demonstrate the presence of functional binocular cortical mechanisms in patients with MFS. The findings are consistent with the hypothesis that elicitation of this class of BVEPs requires gross sensory fusion, but not fine stereoscopic vision.