Pretectal pseudobobbing. Five patients with 'V'-pattern convergence nystagmus.

Five patients with acute obstructive hydrocephalus experienced arrhythmic, repetitive downward and inward eye movements at a rate ranging from one per three seconds to two per second and an amplitude of one fifth to one half of the full voluntary range. Because of a faster downstroke and appropriate amplitude, these movements were usually diagnosed as ocular bobbing. However, their "V" pattern, the generally faster rate, and pretectal, rather than pontine-associated, signs distinguished them from true ocular bobbing. This pretectal pseudobobbing probably represents a variety of convergence nystagmus, and in contrast with true pontine bobbing, usually indicates a need for prompt surgical attention.