Nystagmus is an involuntary
rhythmic oscillation of one or both eyes (see Table 24.2). The direction of the
fast phase, the frequency and amplitude of the nystagmus should be noted.
Acquired nystagmus always requires investigation (neuro-imaging and/or
electrophysiology). Nystagmus may also occur if there is muscle paralysis or
weakness (e.g. secondary to myasthenia gravis).