Saccade and smooth-pursuit impairment after cerebral hemispheric lesions.

A number of cortical and subcortical areas are involved in the control of saccades and smooth pursuit, and lesions affecting these areas result in various ocular motor syndromes. Most of these syndromes are relatively subtle and have to be ascertained using recordings, because other brain areas may largely take over the function of a damaged area. Anterior cortical, posterior cortical, large and bilateral cortical, subcortical and degenerative cerebral lesions are successively reviewed. In the anterior part of the cerebral hemisphere, the frontal eye field (FEF), supplementary eye field (SEF) and prefrontal cortex (PFC), i.e. area 46 of Brodmann, control eye movements. The FEF appears to be principally involved in the control of intentional saccades, in particular those made with a retinotopic reference system, and in smooth pursuit. The SEF could control saccades made with a spatiotopic reference system, and sequences of saccades (requiring a temporal working memory). The PFC could control the inhibition of unwanted reflexive saccades, and be involved in spatial memory used for programming all types of memory-guided saccades. In the posterior part of the cerebral hemisphere, the parietal eye field (PEF) is involved in the triggering of reflexive visually guided saccades, and the middle temporal (MT) and medial superior temporal (MST) areas in smooth pursuit. Acute and large unilateral lesions usually result in transitory ipsilateral conjugate eye deviation. Bilateral lesions affecting both the FEF and the PEF result in severe saccade and smooth-pursuit paresis, whereas bilateral posterior temporoparietal lesions result in Balint's syndrome, consisting of both eye movement and visual-attention abnormalities. Subcortical lesions also result in various eye movement abnormalities, which have been little documented to date. Lastly, degenerative cerebral diseases, such as Alzheimer's disease, Parkinson's disease, Huntington's disease, progressive supranuclear palsy and corticobasal degeneration result in more or less severe eye movement disturbances. Eye movement recordings may contribute to early differential diagnosis of some of these degenerative diseases.