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O. Bergamin, M. Piccirelli, R. Luechinger, V. Sturm, P. Boesiger, K. Landau; Motion-Encoded MRI of the Horizontal Extraocular Muscles: New Insights. Invest. Ophthalmol. Vis. Sci. 2008;49(13):4494.
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Motion-encoded MRI1 has a great potential to analyse extraocular muscle (EOM) movements in health and disease. We studied the deformation pattern along the horizontal EOMs in seven healthy subjects and in a patient with Duane’s syndrome type 1.
All subjects gazed at a horizontal sinusoidal moving target (2s period, peak velocity 64°/s, amplitude ±20°) during four minutes and 30s. One orbit of each subject was imaged with motion encoding techniqe1. The optic nerve (ON) and the horizontal rectus muscles were tracked with an improved mesh algorithm. The local changes of length of the mesh along the EOMs and the ON were investigated for both gaze directions.
In the seven healthy subjects the EOM deformation patterns during left to right and right to left gaze were similar and therefore suggest both horizontal muscles to be active during smooth pursuit. The variability was smaller than 10%. The deformation along the lateral rectus muscle of the patient with Duane’s syndrome revealed the anterior muscle segment to have different contraction and relaxation patterns than the posterior segment.
Motion-encoded MRI technique as used in this study resolved the dynamics of the differential contraction and relaxation of extraocular muscle segments in healthy subjects and differentiated the pathologic from the physiologic pattern. The loss of functionality was assigned to specific EOM segments.Reference: 1) Piccirelli, M., Luechinger, R., Rutz, A.K., Boesiger, P., & Bergamin, O. (2007). Extraocular muscle deformation assessed by motion-encoded MRI during eye movement in healthy subjects. Journal of Vision, 7(14):5, 1-10, http://journalofvision.org/7/14/5/, doi:10.1167/7.14.5.
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