An Anatomical Study of the Inferior Oblique Muscle: The Embalmed Cadaver vs the Fresh Cadaver

doi:10.1016/j.ajo.2008.09.012

American Journal of Ophthalmology

Volume 147, Issue 3, March 2009, Pages 544-549.e1

https://doi.org/10.1016/j.ajo.2008.09.012 Get rights and content

Purpose

To determine the incidence of divided bellies of the inferior oblique (IO) muscle in embalmed and fresh cadavers, and to elucidate the symmetry of IOs in the left and right eyes.

Design

Cohort study.

Methods

IOs were dissected from their origin to the insertion point in 40 intact orbits of 20 embalmed cadavers and in 22 intact orbits of 11 fresh cadavers. The width and location of the IO origin were measured in the skull. In addition, the locations and patterns of IO insertions on the globe were recorded.

Results

Divided bellies were evident in 18 of the 40 IOs (45%) in the 20 embalmed cadavers but in none of the 22 IOs in the 11 fresh cadavers. The insertional patterns of the IOs differed between the left and right eyes in 12 of 31 cadavers (39%).

Conclusions

Dehiscence attributable to the loss of intermuscular fatty tissue and shrinkage in the postmortem state could be mistaken for actual divided bellies in embalmed cadavers. Future studies should investigate the incidence of multiple insertions of IOs in a large number of fresh cadavers. In addition, ocular surgeons should be aware of the possibility of differences in the insertional anatomy of IOs between the left and right eyes.

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Methods

Thirty-one cadavers were obtained with permission from the Anatomy and Cell Biology Department at Hanyang University. The age at the time of death was 63 ± 16 years (mean ± standard deviation). All cadavers were registered with Hanyang University, and appropriate consents and approvals were obtained prior to use.

This study involved 40 intact orbits of 20 embalmed adult cadavers, and 22 orbits of 11 fresh cadavers (with no formaldehyde preservative used) that had not previously been thawed. The

Inferior Oblique Muscle Anatomic Variables in Embalmed and Fresh Cadavers

The distances from the apex of the lacrimal fossa and from the inferior orbital rim to the origin of the IO were 17.48 ± 1.92 mm and 1.08 ± 0.82 mm, respectively. The width of the origin was 2.72 ± 0.78 mm, and the angle between the IO and the inferior orbital rim was 28.87 ± 10.51 degrees (Figure 1). The width of the muscle belly was 7.08 ± 1.14 mm, and the neurovascular bundle entered the IO at 17.15 ± 2.99 mm from the insertion. The width of the IO insertion was 9.27 ± 1.35 mm. The distances

Discussion

The anatomic studies of Fink¹ on the oblique muscles have been followed by many studies on IO anatomy, especially regarding the insertional patterns, for which a wide range of incidence rates of multiple insertions and bellies has been reported (2% to 91.7%).2, 3, 4, 5, 6, 7, 8, 9 In our study, divided bellies of IOs were found in 27.4% of the total cadaveric orbits examined.

There are several possible reasons for the diverse results from the previous studies. First, the preservation status of

Sun Young Shin, MD, received her MD from Hanyang University Medical School, Seoul, Republic of Korea in 1997, where she also completed her residency in the Department of Ophthalmology with subsequent sub-speciality training on the pediatric ophthalmology and strabismus. Dr Shin is a former Assistant Professor at the Department of Ophthalmology, College of Medicine, Hanyang University from 2005 to 2007. She is currently an Assistant Professor at the Department of Ophthalmology and Visual Science