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S. P. Christiansen, R. S. Antunes-Foschini, L. K. McLoon; The Effects of Recession Surgery vs. Tenotomy Without Recession on Myosin Expression and Satellite Cell Activity in Rabbit Extraocular Muscle. Invest. Ophthalmol. Vis. Sci. 2010;51(13):5824.
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In recession surgery, an extraocular muscle (EOM) tendon is moved posterior to its anatomic insertion. This decreases resting tension across the agonist-antagonist pair, diminishes the mechanical advantage of the muscle, and rotates the eye opposite the recessed muscle. Tenotomy without recession, used by some for nystagmus surgery, could provide a useful comparison for the reported effects of EOM recession. We examined the effects of these two procedures on satellite cell activity and myosin heavy chain isoform expression.
The tendinous insertion of one superior rectus muscle was detached and sutured either 7 mm posterior to its anatomic insertion (recession) or at the same site (tenotomy). After 7 or 14 days, the rabbits received injections of bromodeoxyuridine (brdU) every 2 hours for 12 hours followed by a 24 hour brdU-free period. The 3 groups of superior rectus muscles (recessed, tenotomized, control) were examined for Pax7 expression, brdU incorporation, and changes in myosin heavy chain (MyHC) isoform expression.
Recession surgery resulted in increased numbers of brdU-positive satellite cells in both the orbital and global layers after 1 and 2 weeks, while tenotomy only caused increases in brdU-positive cells in the global layer. Recession surgery resulted in little change in fast MyHC expression, decreasing in the global layer at 2 weeks; however, there were significant increases in the number of slow MyHC fibers. Tenotomy resulted in changes only in the orbital layer at one week, with a decrease in fast and an increase in slow MyHC expressing fibers. Neonatal MyHC decreased in both layers one week after both types of surgery. After two weeks, the recessed muscle had significant increases in neonatal MyHC fibers in both layers, while the tenotomy muscles had returned to normal values. Developmental MyHC decreased in only the global layers of the recessed muscles, and tenotomy had no effect on this isoform.
Increased myofiber expression of slow myosin and decreased immature MyHC expression occurred after recession surgery. Tenotomy had less effect on MyHC expression; when changes were seen, they were short-lived. Recession also results in activation of satellite cells in both global and orbital muscle layers. Tenotomy results in increases only in the global layer. These differential adaptive responses may allow further manipulation to improve surgical success rates.
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