Nystagmus: diagnostic and therapeutic strategies.

Nystagmus can have either a jerk (slow and quick phase) or a pendular waveform. Saccadic oscillations can either be back-to-back saccades or have an interval between two saccades. Both nystagmus and oscillations can decrease visual acuity and cause oscillopsia. Each type of nystagmus is attributable to instability or an inadequacy of specific ocular motor systems, including vestibular, optokinetic, smooth pursuit, fixation and the neural integrator. Saccadic oscillations are attributable to instability of the saccadic system. Nystagmus that develops during infancy will not decrease visual acuity if the foveation time within each slow phase is adequate (>60 msec). Infantile nystagmus also does not cause oscillopsia, possibly because the internal spatial visual map is reupdated before each phase of this type of nystagmus (efference copy). There is no foveation period or adequate efference copy reupdate in acquired nystagmus. Consequently, acquired nystagmus usually results in decreased visual acuity and oscillopsia. For most forms of treatment, the goal is directed toward stopping the oscillations or their visual consequences rather than towards the underlying mechanism. Several treatment modalities have been suggested. The most success has been found with gabapentin in the treatment of acquired pendular nystagmus and baclofen in the treatment for acquired periodic alternating nystagmus. There is a need for multicenter trials to evaluate systematically potential treatments of the other types nystagmus and oscillations.