Clark R A, Miller J M, Demer J L
Department of Ophthalmology, University of Califormia, Los Angeles 90095-7002, USA.
Invest Ophthalmol Vis Sci. 1997 Jan;38(1):227-40.
The paths of the rectus extraocular muscles (EOMs) are constrained by pulleys, connective tissue sleeves mechanically coupled to the orbital walls. This study sought to investigate, using high-resolution magnetic resonance imaging (MRI), the location and stability of EOM pulleys in normal subjects and those with strabismus.
Multiple contiguous coronal MRI scans spanning the anterior-to-posterior extent of the orbit during primary gaze, upgaze, downgaze, adduction, and abduction were analyzed digitally to determine the paths of the rectus EOMs. Pulley locations were inferred from EOM paths.
Data for 10 orbits of six normal subjects established the normal paths of the rectus extraocular muscles in primary gaze. Muscle paths in primary position were highly uniform across normal subjects. In secondary gaze positions, rectus muscle paths at the level of the pulleys exhibited small but consistent shifts, relative to the orbit, opposite the direction of gaze, consistent with the expected mechanical effects of the intermuscular connective tissue suspensions of the pulleys. Twelve orbits of seven subjects with strabismus showed, as a group, no significant difference from normal in rectus muscle paths in primary gaze and no significant difference from normal in changes of muscle paths in secondary gaze. Two subjects with incomitant strabismus wer found to have grossly abnormal rectus muscle paths in primary gaze, suggesting heterotopic pulleys. Computer simulations of these heterotopic pulley locations accounted for the observed patterns of incomitant strabismus in both.
High-resolution MRI can determine the location and sideslip of rectus EOM pulleys. Pulley position is highly uniform across normal subjects, consistent with the notion that musculo-orbital tissue connections determine the pulling direction of the rectus EOMs. In normal subjects and subjects with strabismus, pulleys exhibit small shifts with eccentric gaze that are consistent with secondary intermuscular, but not musculo-global, mechanical couplings. Heterotopic pulley position is a potential cause of incomitant strabismus.
眼外直肌（EOMs）的走行受滑车限制，滑车是与眶壁机械连接的结缔组织套。本研究旨在使用高分辨率磁共振成像（MRI）研究正常受试者和斜视患者眼外肌滑车的位置和稳定性。
对在第一眼位、上视、下视、内收和外展时跨越眼眶前后范围的多个连续冠状面MRI扫描进行数字分析，以确定直肌眼外肌的走行。从眼外肌走行推断滑车位置。
6名正常受试者的10个眼眶的数据确定了第一眼位时眼外直肌的正常走行。正常受试者在初始位置的肌肉走行高度一致。在第二眼位时，滑车水平的直肌走行相对于眼眶表现出小但一致的偏移，与注视方向相反，这与滑车的肌间结缔组织悬吊带的预期机械效应一致。7名斜视患者的12个眼眶作为一组，在第一眼位时直肌走行与正常无显著差异，在第二眼位时肌肉走行变化与正常无显著差异。发现2名非共同性斜视患者在第一眼位时直肌走行明显异常，提示滑车异位。对这些异位滑车位置的计算机模拟解释了两者中观察到的非共同性斜视模式。
高分辨率MRI可以确定直肌眼外肌滑车的位置和侧滑。滑车位置在正常受试者中高度一致，这与肌眶组织连接决定直肌眼外肌牵拉方向的观点一致。在正常受试者和斜视患者中，滑车在偏心注视时表现出小的偏移，这与继发性肌间而非肌-整体机械耦合一致。异位滑车位置是导致非共同性斜视的一个潜在原因。
