Pathological torsional eye deviation during voluntary saccades: A violation of Listing's law

Background - Under normal conditions, there are no torsional eye movements during voluntary saccades when the head is stationary (Listing's law). Methods and results - Using dual search coils for three dimensional eye movement recordings, a patient is reported who had direction specific rapid deviations of torsional eye position (up to 10.5°) during voluntary saccades followed by a slow exponential torsional drift after the end of the saccade ('blip') towards the initial torsional eye position. In the absence of spontaneous nystagmus, this transient torsion means a violation of Listing's law for voluntary saccades and was associated with a lesion involving the cerebellar vermis, its deep nuclei, and the dorsolateral medulla. Amplitudes of the blip were larger for ipsilesional (hypermetric) than contralesional (hypometric) horizontal saccades. For comparison transient torsion during and after saccades was also examined in six normal subjects. Using the same in vivo calibration, there were no blips larger than 1.2°in any of them. Conclusion - Transient torsion with large amplitudes can be clinically seen on bedside examination and might thus be a new clinical sign in the diagnosis of saccadic disorders.