This group of phasic or repetitive eye movements is distinguished from nystagmus in that each is composed of abnormal saccades without intervening slow phase eye movements. Opsoclonus is the term applied to rapid, conjugate oscillations of the eyes in horizontal, rotatory, and vertical directions, often made worse by voluntary movement or the need to fixate the eyes. These movements are continuous and chaotic, without an intersaccadic pause (hence the colorful term saccadomania). They can be observed even when the eyes are closed, and often persist in sleep. As indicated in Chap. 4, they are usually part of a widespread myoclonus associated with paraneoplastic or parainfectious disease. In adults, lung, breast, and testicular cancer are important considerations, while in children an evaluation for neuroblastoma is essential (see “Paraneoplastic Cerebellar Degeneration” discussed in Chap. 30). Other less frequent causes include HIV, poststreptococcal infection, West Nile virus encephalitis, and rickettsial infections. Opsoclonus may also be observed in patients who are intoxicated with antidepressants, anticonvulsants, organophosphates, cocaine, lithium, thallium, and haloperidol; in the nonketotic hyperosmolar state; and in cerebral Whipple disease, where the eye movements are coupled with rhythmic jaw movements (oculomasticatory myorhythmia). A benign childhood form can persist for years without explanation and is responsive to adrenocorticotropic hormone (ACTH), as in the “dancing eyes” syndrome of Kinsbourne. In addition, a self-limited benign form exists in neonates.
Ocular flutter refers to intermittent bursts of very rapid horizontal oscillations around the point of fixation; this abnormality is also associated with cerebellar disease. Flutter at the end of a saccade, called flutter dysmetria (“fish-tail nystagmus”) has the appearance of dysmetria, but careful analysis indicates that it is probably a different phenomenon. Whereas the inaccurate saccades of ocular saccadic dysmetria (an ataxic phenomenon) are separated by a brief pause (intersaccadic interval), flutter consists of consecutive saccades without an intersaccadic interval; that is, back-to-back saccades (Zee and Robinson). All those movements have the same implication of cerebellar cortical disease. One hypothesis relates opsoclonus and ocular flutter to a disorder of the saccadic “pause neurons,” but their exact anatomic basis has not been elucidated. Similar movements have been produced in monkeys by creating bilateral lesions in the pretectum. Some normal individuals can voluntarily induce flutter for brief periods, but the movement cannot be sustained (voluntary “nystagmus”).
Square wave jerks refer to involuntary saccades that disrupt fixation. The eyes are seen to horizontally move off target, pause for approximately 200 ms, and then move back. The term square wave jerks comes from a description of the recording of these eye movements. Square wave jerks can be a normal finding in the elderly, but their frequency becomes increased many conditions, particularly neurodegenerative disorders such as progressive supranuclear palsy.
An eye movement difficult to classify is ocular neuromyotonia that is found after radiation that includes the field of the ocular motor nerves (and less characteristically from vascular or tumor compression). There is intermittent diplopia owing to paroxysmal contraction of one or more ocular muscles, usually after their activation. Like superior oblique myokymia (discussed earlier), ocular neuromyotonia may respond to anticonvulsant medications such as carbamazepine.
Disorders of the Eyelids and Blinking