An anatomical study of the inferior oblique muscle with emphasis on its nerve entry

Background: Anatomical studies regarding the inferior oblique muscle are scarce and the exact location of the entry of oculomotor nerve to the muscle has not been reported. In the present study, the objectives were to examine the exact location of the entry of oculomotor nerve to the inferior oblique muscle and to study the topographical anatomy of the muscle. Methods: The study included 56 intact orbits from 28 embalmed south Indian adult cadavers. The entire course of the nerve to the inferior oblique was exposed from both anterior and posterior aspects in all specimens. The exact location of the entry of nerve supplying the inferior oblique muscle was identified and the distances of the muscle from inferior and medial orbital margins were measured. Results: The oculomotor nerve entered the inferior oblique muscle through the orbital surface in 42 (75%) cases, through the ocular surface in 10 (17.9%) cases and through the posterior border in 4 (7.1%) cases. The distance of the muscle from the inferior orbital margin was 1 mm in majority (78.5%) of the cases. The distance of the muscle from the medial orbital margin was 11 mm in majority (42.8%) of the cases. Conclusion: The present study reports that the oculomotor nerve most often enters the inferior oblique muscle through its orbital surface. Detailed knowledge of the topographical anatomy of inferior oblique muscle and its site of nerve entry are essential for surgeons when performing ophthalmological surgery and regional anesthesia.