purpose: to evaluate the change in ocular motility and muscle thickness measured with ultrasonography after intramuscular injection of bupivacaine and botulinum toxin a. methods: eight patients (five female) were enrolled to measure ocular motility prior and 1, 7, 30 and 180 days after one injection of 2 ml of 1.5% bupivacaine and 2.5 u of botulinum toxin a in agonist and antagonist muscles, respectively, of eight amblyopic eyes. muscle thickness was measured prior and on days 1, 7 and 30 after injection using 10-mhz ultrasonography (eyelid technique). results: mean change in alignment was 10 prism diopters after 180 days (n=6). an average increase of 1.01 mm in muscle thickness was observed after 30 days of bupivacaine injection and 0.28 mm increase was observed after botulinum toxin a injection, as measured by ultrasonography. lateral rectus muscles injected with bupivacaine had a mean increase of 1.5 mm in muscle thickness. conclusion: in this study, a change in ocular motility was observed after 180 days of intramuscular injection of bupivacaine and botulinum toxin in horizontal extraocular muscles. overall, there was an increase of muscle thickness in both botulinum toxinum a and bupivacaine injected muscles after 30 days of injection when measured by ultrasonography. this change was more pronounced on lateral rectus muscles after bupivacaine injection.