Intramuscular Nerve Distribution of the Inferior Oblique Muscle

ABSTRACT

Purpose: The intramuscular nerve distribution in the extraocular muscles is important for understanding their function. This study aimed to determine the intramuscular nerve distribution of the oculomotor nerve within the inferior oblique muscle (IO) using Sihler’s staining.

Method: Seventy-two IOs from 50 formalin-embalmed cadavers were investigated. The IO including its branch of the oculomotor nerve was finely dissected from its origin to its insertion point into the sclera. The total length of the muscle and its width were measured. The intramuscular nerve course was investigated after performing Sihler’s staining, which is a whole-mount nerve-staining technique that stains the nerves while rendering other soft tissues either translucent or transparent.

Results: The total length of the muscle and muscle width were 30.0 ± 2.8 mm (mean±standard deviation), 8.8 ± 1.2 mm, respectively. The oculomotor nerve enters the IO around the middle of the muscle and then divides into multiple smaller branches without distinct subdivisions. The intramuscular nerve distribution within the IO has a root-like arborization and supplies the entire width of the muscle. The Sihler’s stained intramuscular nerve course (covering a length of 7.6 ± 1.2 mm) finishes around the distal one-third of the IO in gross observations.

Conclusion: Sihler’s staining is a useful technique for visualizing the gross nerve distribution of the IO. This new information about the nerve distribution and morphological features will improve the understanding of the biomechanics of the IO.

KEYWORDS:

• Inferior oblique muscle
• intramuscular nerve distribution
• Sihler’s stain
• oculomotor nerve
• botulinum toxin injections

Acknowledgments

The authors express their gratitude to the donor cadavers and their families who participated in the medical school cadaveric donation program.

Author Contributors

Hyun Jin Shin designed this study and wrote the manuscript

Shin-Hyo Lee collected the data, drew the illustration and revised this manuscript

Tae-jun Ha collected the data

Wu-Chul Song designed this study and

Ki-Seok Koh designed this study and revised this manuscript

Conflicts of interest

No conflicting relationship exists for any author

Additional information

Funding

This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIT) [No. NRF-2019R1F1A1059435].