Evidence Supporting Extraocular Muscle Pulleys: Refuting the Platygean View of Extraocular Muscle Mechanics

BACKGROUND Late in the 20th century, it was recognized that connective tissue structures in the orbit influence the paths of the extraocular muscles and constitute their functional origins. Targeted investigations of these connective tissue “pulleys” led to the formulation of the active pulley hypothesis, which proposes that pulling directions of the rectus extraocular muscles are actively controlled via connective tissues. PURPOSE This review rebuts a series of criticisms of the active pulley hypothesis published by Jampel, and Jampel and Shi, in which these authors have disputed the existence and function of the pulleys. METHODS This article reviews published evidence for the existence of orbital pulleys, the active pulley hypothesis, and physiological tests of the active pulley hypothesis. Magnetic resonance imaging in a living subject and histological examination of a human cadaver directly illustrate the relationship of pulleys to extraocular muscles. RESULTS Strong scientific evidence is cited that supports the existence of orbital pulleys and their role in ocular motility. The criticisms of the hypothesis have ignored mathematical truisms and strong scientific evidence. CONCLUSIONS Actively controlled orbital pulleys play a fundamental role in ocular motility. Pulleys profoundly influence the neural commands required to control eye movements and binocular alignment. Familiarity with the anatomy and physiology of the pulleys is requisite for a rational approach to diagnosing and treating strabismus using emerging methods. Conversely, approaches that deny or ignore the pulleys risk the sorts of errors that arise in geography and navigation from incorrect assumptions such as those of a flat (“platygean”) earth. J Pediatr Ophthalmol Strabismus 2006;43:296-305. AUTHOR The author is from the Departments of Ophthalmology and Neurology, Jules Stein Eye Institute, and Bioengineering and Neuroscience Interdepartmental Programs, University of California, Los Angeles, Los Angeles, California. The author is the Leonard Apt Professor of Ophthalmology. Originally submitted July 10, 2006. Accepted for publication August 1, 2006. Address reprint requests to Joseph L. Demer, MD, PhD, Jules Stein Eye Institute, 100 Stein Plaza, UCLA, Los Angeles, CA 90095-7002. Supported by U.S. Public Health Service, National Eye Institute grants EY13583, EY08313, and EY00331, and an unrestricted award from Research to Prevent Blindness.