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HC Lee, SY Oh; The Changes in the Structure and Myosin Heavy Chain Expression in the Global and Orbital Layers of the Extraocular Muscle After Extraocular Muscle Tenotomy . Invest. Ophthalmol. Vis. Sci. 2002;43(13):1456.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: Extraocular muscle (EOM) consists of two layers, which are readily distinguished by their histopathology. This study was conducted to investigate the changes of histopathology, myosin heavy chain (MHC), and MHC isoforms of the global and orbital layers of EOM after tenotomy. Methods: Twenty-four New Zealand white rabbits were used. The rectus muscles were harvested on day 3, week 1, week 2, week 4, and week 8 after EOM tenotomy. The change of EOM mass was measured. The EOM were serially sectioned in the coronal plane and stained with Masson's trichrome. The diameters of the muscle fibers and cross sectional areas of the two layers were measured in the middle of the muscles. The change of MHC amount was measured using an electrophoresis. The changes of MHC isoforms were also measured qualitatively and quantitatively using immunohistochemistry and western blot immunostaining. Results: The EOM mass decreased at all periods of the surgery especially on day 3 and week 1. The diameters of EOM fibers in the global layer decreased at day 3, week 1, and week 2 after EOM tenotomy. But there were no significant changes in the orbital layer. The proportions of the cross sectional areas had the same results as the EOM diameters. The immunohistochemical stains of fast and slow MHC had weakened in the global layer at week 1 after tenotomy. The amount of MHC decreased at all periods of the surgery and decreased 62.8% at week 1 after tenotomy. The amounts of fast and slow MHC decreased at all periods after tenotomy. However, no significant difference was found between the control and tenotomy group in regards to the amount of neonatal and developmental MHC. Conclusion: Changes to EOM due to the atrophy of EOM are thought to have appeared at day 3, week 1, and week 2 after EOM tenotomy while EOM atrophy recovered at week 4 and week 8 after the surgery. These changes did not appear on the EOM orbital layer but to the EOM global layer. These results were due to the histological and functional differences of the EOM global and orbital layers.
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