RESUMO
Subconjunctival injection of gentamicin(R)(GM) can cause an acute myopathy of the extraocular muscles. The purpose of this study is to demonstrate the effect of various dosage of GM and reversibility of tissue changes after subconjunctival injection of GM with 10m/ml, 20mg/ml and 40mg/ml each rabbit respectively. We obtained the superior rectus at 1 day, 1 week, 4 weeks and 12 weeks after injection and examined the specimens by light and electron microscopes. On 1 day, light microscopy showed inflammatory change with polymorphonuclear leukocytes and monocytes on 1 week. The higher the concentration of GM was, the more marked inflammation and degeneration of the muscle fibers were. The control group was normal. On 4 weeks there were markedly regenerated muscle fibers with focal degeneration. On 12 weeks there were nearly normal finding of the muscle with some degeneration. On 1 day and 1 week, electron microscopy showed various degrees of degeneration of the muscle fibers. On 4 and 12 weeks the muscle fiber showed satellite nucleus, deposit of abundant Golgi networks, increased numbers and enlargement of mitochondria with some degeneration. On early stage of injecton with normal saline, some vacuoles were seen in the control group. Our results suggest that gentamicin-induced myopathy is dose-related and reversible in histological aspect.