Bilateral ptosis due to mesencephalic lesions with relative preservation of ocular motility.

Three cases of bilateral ptosis with relatively normal ocular motility are presented. In two of the patients, neuroimaging demonstrated lesions in the region of the third cranial nerve subnuclei. These unusual clinical presentations are due to isolated involvement of the central caudal nucleus supplying the bilateral levator muscles, with, virtually complete sparing of other third cranial nerve structures.