Bupivacaine injection myotoxicity on extraocular muslces. A strabismus alternative treatment: extended histological changes induced in a rabbit model.

Purpose: To evaluate longer term histological changes of extraocular muscles induced by bupivacaine toxicity.

Methods: The superior rectus and inferior rectus of white rabbits were injected with 0.4 mg of agent in 0.3 ml of bupivacaine., Then, histological changes of these rectus muscles were examined at 1,2,4 and 8 weeks after injection.

Results: Bupivacaine injection induced myotoxic changes in both orbital and global layers. Regenerating myofibers were found at 1 week after injection. These changes were reduced by 4 weeks post injection. At 4 weeks increasing muscle fiber size in both orbital and global layer were seen. There was no scar formation after 8 weeks post injection.

Conclusions: Extraocular muscle bupivacaine injection can cause acute myonecrosis followed with regeneration. After 8 weeks the muscles recovered with arranged myofibers almost at normal level. However we found increased myofiber diameter at 4 weeks after injection which was remained stable until 8 weeks post injection, Further investigation about functional change in these muscles is needed to facilitate application of this methodology.