One-Month-Old Rabbits Exhibit a Longer Postoperative Remodeling in Extraocular Muscles Compared to 3-Month-Old Rabbits.

Purpose: To explore whether there is a difference in postoperative extraocular muscle (EOM) remodeling between 1-month-old and 3-month-old rabbits.

Methods: Recession (n = 16) and resection (n = 16) were performed on the right superior rectus (SR) muscles of 1-month-old and 3-month-old rabbits. SR tissues were harvested 1 and 4 weeks post-surgery (n = 4 for each group), and mid-belly sections were used to assess myosin heavy chain (MyHC) isoform expression (fast 2X, embryonic, and neonatal MyHCs), activated satellite cells (SCs), and centrally nucleated myofibers. Age-matched unoperated rabbits (n = 4) served as controls.

Results: In 1-month-old rabbits, fast 2X-MyHC expression continuously decreased post-recession (all P < 0.01), and embryonic MyHC expression increased both post-recession and post-resection (all P < 0.01), except in the global layer (GL) post-resection. In 3-month-old rabbits, fast 2X-MyHC decreased at 1 week post-recession (in both layers P < 0.01) but returned to preoperative levels by 4 weeks (in both layers P = 1). Embryonic MyHC remained stable (P = 0.239) or increased (in the GL post-recession and in the orbital layer (OL) post-resection, both P < 0.001) at 1 week postoperatively, except in the GL post-resection. It had returned (in the GL post-recession, P = 0.952; in the GL post-resection, P = 0.574) or nearly returned (in the OL post-resection, P = 0.038) to preoperative levels in both layers by 4 weeks. Activated SCs in 1-month-old rabbits continuously increased post-surgery (all P < 0.05), except in the OL post-resection. In 3-month-old rabbits, SCs remained stable at 1 week but decreased by 4 weeks post-surgery (all P < 0.01), except in the OL post-resection. Centrally nucleated myofibers were more prevalent in 1-month-old rabbits by 4 weeks postoperatively.

Conclusions: One-month-old rabbits displayed longer postoperative remodeling and greater plasticity in EOMs than 3-month-old rabbits. The difference in postoperative remodeling may impact strabismus surgery outcomes in patients of different developmental stages.