Anatomical study on branching pattern and variations of orbital segment of the oculomotor nerve

BACKGROUND: This study aims to revisit the anatomy of orbital segment of the third cranial nerve (CN III). The study also involved morphometric measurements of CN III muscular branches. Detailed description of observed anatomical variations and their incidence was also included. The study supplements earlier findings with detailed observations of the neuromuscular relations. MATERIALS AND METHODS: The study was conducted on 52 orbits taken from 26 cadaveric heads (10 males and 16 females; Central European population). RESULTS: Anatomical variations of the orbital segment of the CN III observed on the examined material involved both the superior and inferior branch of this nerve. The muscular branch innervating the levator palpebrae superioris muscle occasionally pierces the superior rectus muscle. The nerve to the inferior oblique muscle may pierce and innervate the inferior rectus muscle. In rare instances, duplication of the parasympathetic root of the ciliary ganglion may also occur. Among the muscular branches, the smallest diameter reached the branch to the levator palpebrae superioris muscle. Among the three muscular branches derived from the inferior branch of the CN III, the nerve to the inferior oblique was the longest one. Its length varied from 28.9 mm to 37.4 mm. The shortest was the muscular branch to the inferior rectus muscle. Its length varied from 0 mm (when muscular sub-branches arose directly from the nerve to the inferior oblique muscle) to 7.58 mm. CONCLUSIONS: This study presented the characteristic of orbital segment of the CN III, including anatomical variations and morphometric measurements relevant to intraorbital procedures.