Rotational vertebral artery syndrome: oculographic analysis of nystagmus.

In four patients with rotational vertebral artery syndrome (RVAS), the initial nystagmus was mostly downbeat, with the horizontal and torsional components beating toward the compressed vertebral artery side (n = 3) or directed away (n = 1). Three patients showed spontaneous reversal of the nystagmus and two exhibited no or markedly diminished responses on immediate retrial of head rotation (habituation). The patterns of nystagmus suggest that RVAS may result from differing mechanisms.