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S. Park, Y. Kim, J. Lee, S.–Y. Oh; The Changes of Muscle Fiber in Size and in the Composition of Myosin Heavy Chain Isoforms in Global and Orbital Layers After Extraocular Muscles Recession . Invest. Ophthalmol. Vis. Sci. 2006;47(13):5060.
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© ARVO (1962-2015); The Authors (2016-present)
To assess the changes of the size of muscle fiber and the composition of myosin heavy chain (MyHC) isoforms in global layers (GL) and orbital layers (OL) of extraocular muscles after recession surgery.
3–mm and 8–mm recessions of superior rectus muscles were performed, each on 12 right eyes of New Zealand white rabbits. Among each 12 right eyes, 4 were used for measuring cross–sectional areas of muscle fibers after Masson’s trichrome staining, 4 for immunohistochemical staining against MyHC isoforms, and the rest 4 for electrophoresis of MyHC isoforms. 24 fellow eyes were left untouched. Right superior rectus muscles were harvested at 3 days, 1, 2, and 4 weeks after surgery. For Masson’s trichrome and immunohistochemical staining, muscles were cut perpendicularly to the longitudinal axis of muscle belly. In order to quantify each MyHC isoform, electrophoresis of the supernatant from centrifuged muscle homogenate was performed. Right superior rectus muscles harvested from naive rabbits were used as control.
The cross–sectional areas of 19333 muscle fibers – 9523 in OL and 9810 in GL – were measured and analyzed. No significant changes were observed after 3–mm and 8–mm recessions in OL compared with the control. In GL, however, the mean cross–sectional area of muscle fibers decreased significantly at 1 week after surgery and normalized at 2 weeks postoperatively in 3–mm recession group, and it decreased significantly at 3 days, 1 and 2 weeks after surgery and normalized at 4 weeks postoperatively in 8–mm recession group. On electophoresis, the proportion of type IIb in MyHC isoforms increased significantly at 3 days and 1 week after surgery and decreased at 2 weeks postoperatively in 3–mm recession group, and it increased at 3 days, 1 and 2 weeks after surgery and decreased at 4 weeks postoperatively in 8–mm recession group. The changes of proportion of other MyHC isoforms were not notably correlated with the histologic changes of GL after recession surgery.
The change of the muscle fiber diameter after extraocular muscle recession was observed only in GL as transient atrophy and type IIb MyHC seemed to be closely correlated with such change.
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