Effects of stimulus velocity and acceleration on smooth pursuit in motor neuron disease

Sinusoidal smooth pursuit eye movements were evaluated in 11 normals, five moderately and four severely affected motor neuron disease (MND) patients, using two target amplitudes and a range of frequencies. This enabled us to examine separately the effects of peak target velocity and acceleration on pursuit gain. Moderately affected patients showed an acceleration, but not a velocity saturation; severely impaired patients' performance declined with increased velocity. Smooth pursuit eye movements are thus impaired in MND, but the nature of this pursuit deficit is complex and changes with the progression of the disease.