[Diagnosis and clinical assessment of abnormal eye movements]

Abnormal eye movements and nystagmus are, when present, useful for diagnosis of localization of the lesion. Observations of mortality and range of eye movements, pursuit and saccadic eye movements, ability of visual fixation, nystagmus and involuntary eye movements as well as head and eye position, palpebral fissures, ptosis, pupils are important for assessment of eye movements. Anatomical pathways important for horizontal eye movements locate in the caudal pons and for vertical eye movements, in the rostral mesencephalon. In those structures two types of saccade related neurons--burst cells and pause cells-are present and generate premotor saccadic commands. The gaze directed nystagmus results from the central vestibular disorder, not from the peripheral labyrinthine lesion. Bruns' nystagmus characterized by low-frequency, large amplitude nystagmus on looking ipsilaterally and high-frequency, small-amplitude nystagmus on looking contralaterally, is seen in the brainstem lesion. Ocular bobbing consists of rapid downward movement of the eyes followed by a slower return to the primary position and is a sign of pontine lesion. Opsoclonus, multidirectional saccadic oscillation with out intersaccadic interval and flatter-like oscillation, purely horizontal saccadic oscillation are seen in patients with cerebellar and brainstem lesions and may be due to dysfunction of pause cells.