A new clinical technique for demonstrating changes in eye acceleration during horizontal saccades in patients with partial internuclear ophthalmoplegias.
The eyelid-mounted accelerometer can pick up the acceleration waveform of the eye during horizontal eye movements. The acceleration profile comprises high-amplitude pulsatile activity in the saccade and changes in the level of background ocular microtremor related to eye position. Adducting saccades of 20 degrees were recorded in eight patients with partial internuclear ophthalmoplegias caused by multiple sclerosis and in eight age-matched healthy subjects. The initial pulse of acceleration activity was reduced by 85% in the patients. In the worst-affected cases, adducting saccades were associated only with an increase in the level of background ocular microtremor in the acceleration trace. The results confirm the hypothesis that an internuclear ophthalmoplegia is due to the loss of the pulse signal to ocular motor neurons, with preservation of the step signal in an adducting saccade.