Functional imaging of human extraocular muscles in head tilt dependent XXXX .

@entity15170 @entity135 @entity194 @entity75
PURPOSE: Although alteration in @entity15170 induced by head tilt is considered a clinical criterion for diagnosis of superior oblique (SO) palsy, the mechanism of this @entity135 ( @entity135 ) is unclear. In this study, magnetic resonance imaging (MRI) was used to study extraocular muscle (EOM) responses to head tilt in @entity135 . METHODS: Orbital MRI was used to study 16 normal subjects and 22 subjects with HTDT, of whom 12 had unilateral SO @entity194 and 10 had "masquerading" SO palsy with normal SO size. Sizes and paths of all EOMs were compared in 90   roll tilts. RESULTS: Normal subjects exhibited the expected 3   to 7   physiologic extorsion of all four rectus pulleys in the orbit up-versus-down roll positions, corresponding to ocular counterrolling. In orbits with SO @entity194 , the lateral (LR) and @entity75 paradoxically intorted by approximately 2  . Subjects with @entity135 but normal SO size exhibited reduced or reversed extorsion of the medial, superior, and LR pulleys, whereas pulley shift was normal in nonhypertropic fellow orbits in @entity135 . In normal subjects and in SO @entity194 , the inferior oblique (IO) muscle contracted in the orbit up-versus-down roll position, but paradoxically relaxed in @entity135 without SO @entity194 . CONCLUSIONS: The ipsilesional IR and LR pulleys shift abnormally during head tilt in @entity135 with SO @entity194 . In @entity135 without SO @entity194 , the ipsilesional MR, SO, and LR pulleys shift abnormally, and the IO relaxes paradoxically during head tilt. These widespread alterations in EOM pulling directions suggest that complex neural adjustments to the otolith-ocular reflexes mediate @entity135 .
