Less often, exotropia is constant and paralytic, as with infantile exotropia or 3rd (oculomotor) cranial nerve palsy Hypertropia can be paralytic, caused by 4th (trochlear) cranial nerve palsy that occurs congenitally or after head trauma or, less commonly, as a result of 3rd cranial nerve. Treatment may include lubrication of the eye, intermittent use of an eye patch, and, for idiopathic facial nerve palsy, corticosteroids. Hemifacial spasm usually results from nerve compression by a pulsating blood vessel that causes ectopic impulse generation (ephaptic nerve impulses), similar to that in trigeminal neuralgia Unilateral, involuntary, painless contractions of facial muscles usually begin in the eyelid, then spread to the cheek and mouth Contractions may be intermittent at first but may become almost continuous.
Common causes are multiple sclerosis in young people (often bilateral) and stroke in older adults (typically unilateral) Distinguish internuclear ophthalmoplegia (which impairs adduction of the ipsilateral eye but not convergence) from third cranial nerve palsy (which impairs adduction and convergence of the ipsilateral eye). Etiology of myoclonus may be essential (primary), acquired (most common), or idiopathic Essential (primary) myoclonus has no identifiable cause and/or is suspected to involve genetic factors Acquired myoclonus has multiple causes, including many metabolic disorders (see table some causes of myoclonus) Most cases of myoclonus are acquired.
Focal dystonias are common and usually begin during adulthood.
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