A massive sympathetic discharge is largely responsible for the maximal pupillary dilatation that occurs during cerebral ischemia. In addition, it is suggested that a discharge mediated by the ciliary ganglion may also produce pupillary dilatation, at least under experimental conditions.
Paulson GW, Kapp JP. Dilatation of the Pupil in the Cat via the Oculomotor Nerve. Arch Ophthalmol. 1967;77(4):536-540. doi:10.1001/archopht.1967.00980020538018