The accessory oculomotor nucleus contains the visceral motor fibers of the Oculomotor nerve.
Anatomy
The accessory oculomotor nucleus lies mediodorsal to the Oculomotor nucleus.
Function
The efferent fibers of the accessory oculomotor nucleus, all of which travel in the third cranial nerve, provide parasympathetic innervation to the intrinsic muscles of the eye. These are the smooth ciliary muscle and the sphincter pupillae[^1].
Clinical manifestations of a lesion
A lesion of the accessory oculomotor nucleus results in loss of parasympathetic innervation to the eye. Clinically, this manifests as pupillary dilation due to functional predominance of the sympathetic nervous system, which innervates the dilator pupillae. In addition, there is an inability to accommodate due to paralysis of the ciliary muscle. Accordingly, the affected eye develops photophobia and an inability to see near objects clearly. An isolated lesion of the accessory oculomotor nucleus is rare, because the oculomotor nucleus is usually also affected due to its anatomical proximity.