Strabismus much more than orbital pulleys and muscles

Reviewed by Joseph L. Demer, MD, PhD

Los Angeles-There is nothing simple about ocular muscles and sorting out the causes of diplopia and nystagmus. However, recognition of another ocular structure-i.e., pulleys-might make the job a little easier and shift the attention away from the nerves in the orbit.

When physicians learned about how the extraocular muscles (EOMs) are “hooked up” anatomically, they might have assumed that the muscle paths are fixed in the orbit. Therefore, the belief would be that the lateral rectus (LR) muscle always pulls laterally, which would be incorrect, because that belief implies that the muscle sideslips over the globe as it rotates vertically, said Joseph L. Demer, MD, PhD.

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“What is correct is that connective tissue pulleys exist in the orbit at the level of posterior Tenon’s fascia that cause the paths of the muscles to change systematically with gaze,” said Dr. Demer, the Leonard Apt Professor of Ophthalmology and professor of neurology, David Geffen Medical School, and director, Ocular Motility Laboratory, Stein Eye Institute, University of California, Los Angeles.

This is important to ocular motility and it is at least as important as certain neurologic features of the EOMs, he noted.

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Every muscle rotates the eye toward its pulley. In cases in which a pulley is displaced, the muscle can pull the eye in directions other than that intended by a normal pulley. Therefore, Dr. Demer mentioned, not all imbalances of the oblique EOMs result from the oblique muscles.

“So many common forms of strabismus that were presumed to have neurologic origins are actually mechanical,” he said.

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