Abstract
Purpose: :
Surgical recession of extraocular muscles (EOM) is a common treatment for strabismus and other motility disorders. Recession involves the removal of the muscle from its scleral insertion and reattaching the muscle at a point posterior to the original site of insertion. The purpose is to reduce the force of an overacting muscle and restore normal eye position. We examined the effect of this procedure on the activity of satellite cells and myosin heavy chain isoform expression in the recessed extraocular muscle of adult rabbits compared to normal control muscles.
Methods: :
The insertion of the superior rectus (SR) muscle was detached from the sclera and sutured 7 mm posterior to its original insertion site. After 7 days the animals were injected every 2 hours for 12 hours with bromodeoxyuridine (brdU), followed by a 24 hour brdU-free period. The superior rectus muscles were examined for brdU incorporation and neonatal and developmental myosin heavy chain (MyHC) isoform expression changes in the mid-region and tendon ends of the muscles and compared to control superior rectus muscles.
Results: :
In the recessed muscle, the percentage of brdU positive satellite cells in the orbital layers was increased compared to normal control SR muscles, and particularly elevated in the tendon region of the treated muscle. The global layer showed little alteration in satellite cell rates of division, with only a small increase in the tendon end of the global layer. In the global layer of both the middle and tendon ends of the recessed muscles, neonatal and developmental MyHC expression was significantly decreased.
Conclusions: :
Surgical recession of the superior rectus muscle resulted in an increase in satellite cell division at 7 days post-surgery. In contrast to surgical resection, recession surgery resulted in a marked decrease in expression of the immature myosin heavy chain isoforms. This demonstrates that the muscles respond to the reduction in length by remodeling both their myosins and satellite cell activity. It may be possible to improve the post-surgical effects of recession surgery by modulating these processes.
Keywords: extraocular muscles: structure • strabismus • strabismus: treatment