Histopathological changes in extraocular muscles of rabbits following injection of bupivacaine 5mg/Ml versus 7.5mg/Ml.

PURPOSE: To compare the histopathological effects of injecting two concentrations of Bupivacaine (5 mg/ml and 7.5 mg/ml) in the superior rectus muscle of rabbits, and to compare these to conventional extraocular muscle surgery in previous studies.

METHODS

Eighteen albino rabbits' eyes were used. The superior rectus muscles were injected with Bupivacaine 5 mg/ml (Group B5, 10 eyes) or 7.5 mg/ml (Group B7, 8 eyes). The rabbits were sacrificed and eyes enucleated 6 weeks later for histopathological evaluation. Results were compared to the average of those obtained, by three previous studies, after conventional superior rectus resection in rabbits.

RESULTS

Foreign body reaction was absent in all specimens. Conjunctival and scleral inflammation, perimuscular adhesions, intramuscular fibrosis, conjunctival and scleral oedema and muscle atrophy were higher in group B7, while conjunctival hyperaemia and muscle hypertrophy were higher in group B5 (p > 0.05). On comparison to conventional surgery, conjunctival inflammation and hyperaemia, foreign body reaction, and adhesions were less after bupivacaine injection (p > 0.05 for all except for intensity of conjunctival inflammation in B5 versus conventional surgery). Scleral inflammation was more frequent after bupivacaine injection (p < 0.05). Muscle fibrosis was more frequent in group B7 and conventional surgery than in group B5 (p > 0.05).

CONCLUSIONS

Both Bupivacaine concentrations effectively produced the desired muscle hypertrophy and fibrosis, so the lower concentration may be used for muscle strengthening to correct strabismus. Bupivacaine injection, although produced no foreign body reaction, did not significantly lower the development of undesired postoperative adhesions and caused more scleral inflammation.