A neuroanatomical analysis of lid-eye coordination in cases of ptosis and downgaze paralysis.

Ptosis and downgaze paralysis, in a case of vascular insufficiency, were the result of a specific loss of levator palpebrae (LP) motoneurons in the oculomotor nucleus, and a partial cell loss in the rostral interstitial nucleus of the MLF (riMLF), respectively. In a previous case with similar symptoms there was a comparable riMLF cell loss, but some LP motoneurons were spared; in addition there was destruction of a cell group on the mesencephalic midline, which projects to all motoneurons involved in upward eye movements including LP. This cell group is called the M-group in the monkey. The M-group was intact in the present, but not in the previous case, which may have contributed to the ptosis and to the loss of upward ocular pursuit in the latter. The results show that there is more than one premotor cell group responsible for upward eye movements in the rostral mesencephalon.