Bupivacaine injection of the lateral rectus muscle to treat esotropia

PurposeWe report results of a pilot trial of bupivacaine injection into extraocular muscles as a method of enlarging and strengthening the muscles to treat strabismus.MethodsBupivacaine, in volumes from 1.0 to 4.5 mL and concentrations from 0.75% to 3.0%, was injected into 1 lateral rectus muscle in each of 6 patients with comitant esotropia with the use of the electrical activity recorded from the needle tip to guide injection. Magnetic resonance imaging was performed before and at intervals after injection to estimate changes in muscle size. Clinical measures of alignment were made before and at intervals after injection. Two patients required a second injection for adequate effect.ResultsFour patients showed improved eye alignment, averaging 12Δ, measured an average of 367 days after the last injection (range, 244-540 days). Two patients were substantially unchanged. Alignment improvement for all 6 patients averaged 8Δ (range, 0-14Δ). Volumetric enlargement of the injected muscle, computed from magnetic resonance images, was 6.2% (range, –1.5% to 13.3%). There was a positive correlation between alignment change and muscle enlargement averaging 0.65. Injection caused a retrobulbar hemorrhage in an unchanged patient that cleared without affecting vision.ConclusionsBupivacaine injection improved eye alignment in 4 of 6 esotropic patients. There was a positive correlation between improved eye alignment and increased muscle size. Clinical and laboratory studies are underway to determine optimal dosages, effects in other strabismus conditions, and differential effects of bupivacaine on contractile and elastic muscle components.