ABSTRACT
The parasympathetic supply originates in the Edinger-Westphal nucleus, a midline structure situated posterior to the main third cranial nerve nucleus in the upper mid-brain. On leaving the brainstem, the parasympathetic fibres are located in the superior medial portion of the third cranial nerve. They enter the orbit with the inferior division of the third cranial nerve and reach the ciliary ganglion via the nerve to the inferior oblique muscle. After synapsing within the ganglion, the parasympathetic supply arrives at the iris via the short ciliary nerves. The sympathetic supply to the iris is detailed in the Horner’s syndrome topic.
