Ocular motor abnormalities in Huntington's disease

We review here the eye movements in patients with Huntington's disease (HD), concentrating upon saccades as they show the most prominent abnormalities. Inability to suppress reflexive glances to suddenly appearing novel visual stimuli and delayed initiation of voluntary saccades, including predictive saccades, are early and consistent findings. These two abnormalities can be interpreted in the context of a model, based upon the idea that the frontal lobes and basal ganglia contribute more to the control of voluntary than to reflexive types of saccades. Most patients eventually also show slow saccades but they are most prominent when the disease is early-onset. Slowing of saccades may reflect involvement of both the higher-level cerebral centers that trigger saccades and the areas in the brain stem that produce premotor saccade commands. The study of eye movements in HD has led to a fruitful interaction between basic science and clinical investigation, and has served as a paradigm for examining higher-level defects in saccadic eye movement control in patients with various degenerative, neurological diseases or with focal cerebral hemispheral lesions.