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J Neurophysiol (April 1, 2003). 10.1152/jn.00636.2002
Submitted on Submitted 7 August 2002; accepted in final form 9 December 2002
Departments of 1Ophthalmology and 2Neurology, University of California, Los Angeles, California 90095-7002; 3Department of Ophthalmology, Okayama University Medical School, Okayama City 700-8558, Japan; and 4Department of Ophthalmology, University of Texas Southwestern Medical School, Dallas, Texas 75225
Demer, Joseph L.,
Reika Kono, and
Weldon Wright.
Magnetic Resonance Imaging of Human Extraocular Muscles in
Convergence. J. Neurophysiol. 89: 2072-2085, 2003. Extraocular muscle (EOM) paths during asymmetrical convergence
were evaluated by tri-planar, contrast-enhanced magnetic resonance imaging of the orbits of eight young adults during binocular fixation of a target aligned to one eye at 800 and 15 cm distance. Cross sections and paths of EOMs were determined from area centroids. In
convergence, the aligned eye rotated and translated negligibly, while
its inferior oblique (IO) muscle exhibited significant contractile thickening. There were no significant contractile changes in the cross
sections of aligned eye rectus or superior oblique (SO) muscles in
convergence. The converging eye rotated nasally 22.4° but translated
negligibly. The converging eye medial (MR) and lateral rectus (LR)
muscles exhibited large contractile cross-section changes, and the IO
showed significant contractile thickening, while the vertical rectus
muscles and the SO did not. Anterior paths of three aligned eye rectus
EOMs could be determined in convergence and shifted consistent with a
1.9° extorsion of the rectus pulley array. Such extorsional
reconfiguration of the rectus pulleys would move the pulleys in
coordination with globe extorsion and avoid imparting torsional action
to these EOMs. Extorsional rectus pulley shift in convergence is
inconsistent with the reconfiguration predicted to explain the temporal
tilting of Listing's planes, instead suggesting that this temporal
tilting is due to variations in oblique EOM innervation. Absence of
globe translation in convergence argues against overall EOM
co-contraction. The reconfiguration of EOM geometry in convergence has
important implications for single-unit studies of neural control.
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