The application of smooth pursuit eye movement analysis to clinical medicine.

Pursuit tracking eye movements were analyzed from selected patients with neurological injuries and compared to the responses of 20 normal subjects. The patients/subjects tracked a small spot of light moving sinusoidally in the horizontal plane at a frequency of 0.4 Hz and a peak-to-peak amplitude of 40 degrees. Eye-movement responses were separated into a smooth-pursuit component and a saccadic component. The smooth-pursuit component was analyzed by calculating the gain, phase, and asymmetry. The saccadic component was quantified by calculating the percentage of the total tracking movement contributed by the saccadic system. The patients with smooth-pursuit impairment exhibited a higher percentage of saccadic tracking and a lower smooth pursuit gain compared to the normal subjects. One patient with a unilateral lesion exhibited significant asymmetry in the smooth-pursuit component. In this case, the direction of the asymmetry indicated the side of the lesion.