Drug-induced Extraocular Myotoxicity Associated with Diplopia after Cataract Surgery

ABSTRACT

PURPOSE: To assess the myotoxicity of local anesthetics and antibiotics which are considered as the main causes of diplopia and extraocular motility disturbance following cataract surgery. METHODS: A total of 48 rabbits were classified into 4 groups. The control group received an injection of 0.3 ml normal saline in the subconjunctival space above the superior rectus muscle. The first experimental group received an injection of the same amount of a local anesthetic (2% lidocaine) in the same manner as the control group. The second group received an injection of 0.3 ml of a local anesthetic directly into the extraocular muscle (superior rectus muscle), the third group received an injection of 0.3 ml of an antibiotic (gentamicin) in the subconjunctival space above the superior rectus muscle. Histologic and electron microscopic changes following injections were compared over time in each group. RESULTS: Light microscopic findings showed that subconjunctival injections of antibiotics caused the most severe inflammatory and fibrotic reactions of the muscular fascicle, whereas subconjunctival injections of local anesthetics led to the least damage of the muscular fascicle and less infiltration of inflammatory cells. Changes in histological findings showed that necrotic muscle fibers and inflammatory cell infiltration at 1 week following injections. Basophilic myogenous satellite cells indicating regeneration of the damaged muscles appeared thereafter. At 2 and 4 weeks, the group injected with antibiotic showed local and consistent infiltration of inflammatory cells and fibrosis, whereas the groups injected with anesthetics showed regeneration of most of the damaged fascicle. CONCLUSIONS: In terms of temporary or permanent diplopia following an injection of local anesthetics or antibiotics after cataract surgery, toxicity of anesthetics or antibiotics on extraocular muscle is the main cause from these Results.