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V. Das, H. Cheng, M. Swann, A. Narasimhan, M. Mustari, J. L. Demer, T. Q. Duong; MRI Comparison of Extraocular Muscle in Normal Monkeys and Monkeys With Strabismus. Invest. Ophthalmol. Vis. Sci. 2007;48(13):5273.
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© ARVO (1962-2015); The Authors (2016-present)
Investigations based on cellular and genetic methods in monkeys and rats have suggested that sensory disruption of binocular function in infancy may disrupt extraocular muscle (EOM) development. These data imply that sensory induced strabismus may in part be due to disruptions in EOM development. We directly compared gross anatomic properties of EOM in normal and strabismic monkeys to identify whether the proposed genetic/cellular alterations also resulted in changes in EOM size parameters measurable via MRI.
We measured EOM volume using MRI in two normal monkeys, two monkeys with sensory strabismus (strabismus induced via a contact lens rearing paradigm) and two monkeys with surgically induced strabismus (strabismus induced by disinserting the medial rectus muscle bilaterally in the infant). Animals were age and weight-matched (~1 yr old; ~2.5 kilos) at the time of the imaging. Axial, Coronal and Sagittal slices were acquired from anesthetized animals in a 4.7T magnet using T1-weighted sequences with a voxel resolution of 0.227mmX0.227mmX1mm. EOM volume was calculated from 11 contiguous quasi-coronal slices (3 slices anterior to globe-optic nerve junction and 7 slices posterior).
Muscle volumes in the sensory group were uniformly smaller than in normals and surgical strabismics. However medial rectus (MR) volume was approximately equal to lateral rectus (LR) volume (<5% difference) in both normal and sensory groups. Ratio of superior oblique volume to medial rectus volume was similar in the normal and sensory groups suggesting there was no "overaction/underaction of the oblique" in the sensory strabismic animals. In the surgical strabismus animals, the MR was clearly visible and indicated that this muscle had reattached to the globe. However the MR volume was ~15% less compared to the LR volume in these animals.
Our data supports previous reports from our lab and others suggesting that, in animals with sensory strabismus, abnormal alignment and associated eye movements are due to abnormal patterns of innervation and not due to abnormal development of EOM.
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