CONVERGENT DIVERGENT PENDULAR NYSTAGMUS - POSSIBLE ROLE OF THE VERGENCE SYSTEM

We used the magnetic search coil technique to measure horizontal, vert ical, and torsional components of convergent-divergent pendular nystag mus in three patients. All showed phase shifts of approximately 180 de grees between the two eyes in the horizontal and torsional planes, but the vertical components were conjugate. Viewing a near target increas ed the oscillations threefold in one patient and by 60% in a second pa tient. The waveform was sinusoidal in one patient, but in the other tw o it was complex, resembling either a sum of several sine waves or a c ycloid. When the predominant frequency of the nystagmus was low (1.8 H z), oscillation of visually mediated vergence might have been responsi ble; when the frequency was high (6 Hz), the nystagmus might have aris en from an internal instability in connections between nucleus reticul aris tegmenti pontis and cerebellar nucleus interpositus, which are im portant for vergence control.