Does pupillary sparing oculomotor nerve palsy really spare the pupil?

We examined the pupillary cycle time (PCT) in eight elderly patients with isolated oculomotor nerve palsy (ONP) that was characterized by complete involvement of the extraocular muscles. In addition to advanced age, all patients had at least one other vasculopathic risk factor. Although in all cases the pupil was completely spared by clinical impression, the PCT was significantly prolonged compared with the other eye and well outside the normal range (mean 1590 +/- 212 msec on the involved side and 1076 +/- 110 on the uninvolved side). On re-examination, after an interval of 2-3 months, the PCT was either normal or markedly improved in all patients, paralleling the recovery of extraocular muscle function. These findings suggest that even in pure, noncompressive ONPs there is subclinical pupillary involvement. Repeated PCT examinations may provide an objective means to estimate recovery. Moreover, in the problematic subgroup of "pupil sparing" incomplete ONP, PCT monitoring during the first days may indicate possible progression of a compressive lesion.