Elucidated in [[1958]] by Rucker. In effect, the rule states, “[[Third nerve palsy]] due to extrinsic compression of the [[nerve]] will be associated with impaired [[pupillary constriction]].” However, it is often overlooked that in 3% the pupil is spared
((Trobe JD. Third nerve palsy and the pupil. Footnotes to the rule. Arch Ophthalmol. 1988; 106:601–602)).