PURPOSE: To delineate the nature of the nerve capsule to the inferior oblique muscle at birth and adulthood, and to compare it to the nerve capsules of other extraocular muscles. METHODS: Fresh autopsy specimens were obtained from a newborn and a 26 year-old male. The length of the inferior oblique nerve was analyzed with high magnification photomicroscopy and electron microscopy and compared to the nerve capsules of the adult medial, lateral, inferior and superior rectus muscles. These were also compared to the intracranial portion of the third cranial nerve of the adult specimen. RESULTS: The collagen layer of the nerve to the inferior oblique was present throughout its course. It is well developed in the newborn and comparable to the adult specimen. The nerves to the medial, inferior, lateral and superior rectus muscles are also surrounded by a similar capsule containing collagen fibers that are aligned parallel to the axon of the nerve. The intracranial portion of the third cranial nerve only has a thin fibrous capsule. CONCLUSION: The nerve capsule of the inferior oblique comprises a surrounding collagen layer, presumably to protect the nerve from stretching. This layer is well developed along the entire course of the nerve and is present from birth. The nerves to the other extraocular muscles have a similar capsule that likely serves a similar function. These findings expand current understanding of the nerves to the extraocular muscles and may be useful for improving treatments.
PURPOSE: To delineate the nature of the nerve capsule to the inferior oblique muscle at birth and adulthood, and to compare it to the nerve capsules of other extraocular muscles. METHODS: Fresh autopsy specimens were obtained from a newborn and a 26 year-old male. The length of the inferior oblique nerve was analyzed with high magnification photomicroscopy and electron microscopy and compared to the nerve capsules of the adult medial, lateral, inferior and superior rectus muscles. These were also compared to the intracranial portion of the third cranial nerve of the adult specimen. RESULTS: The collagen layer of the nerve to the inferior oblique was present throughout its course. It is well developed in the newborn and comparable to the adult specimen. The nerves to the medial, inferior, lateral and superior rectus muscles are also surrounded by a similar capsule containing collagen fibers that are aligned parallel to the axon of the nerve. The intracranial portion of the third cranial nerve only has a thin fibrous capsule. CONCLUSION: The nerve capsule of the inferior oblique comprises a surrounding collagen layer, presumably to protect the nerve from stretching. This layer is well developed along the entire course of the nerve and is present from birth. The nerves to the other extraocular muscles have a similar capsule that likely serves a similar function. These findings expand current understanding of the nerves to the extraocular muscles and may be useful for improving treatments.