Eye Movement Recordings as a Diagnostic Tool in a Case of Congenital Nystagmus

ABSTRACT Objective recordings of eye movements in a patient with congenital pendular nystagmus showed only tiny superimposed saccades. Also, in tracking movements and in special “variable feedback” experiments, where a normal subject would ordinarily exhibit mainly fair‐sized saccades, the patient showed only markedly decreased saccades. However, these small saccades showed maximal velocities appropriate to their reduced amplitudes: thus suggesting normal “time‐optimal” motor control signal shapes and a normal extra‐ocular muscular system. The increase in pursuit movements seems to be a compensatory effect secondary to the basic defect in saccades. Prisms were prescribed to minimize the amplitude of the nystagmus since it had shown dependence upon angle of gaze and amount of vergence. Excellent subjective results were obtained and indicated that the sensory visual mechanism was normal. Since the efferent signal shape. the muscular system. and the afferent visual system are all normal. and the smooth pursuit system better than normal (compensatory adjustment), we suggest that the basic defect in our patient is early in the generation of intermittent control signals for saccades from the central nervous system dual mode controller.