Diagnostic injection of Xylocaine into extraocular muscles

In situations where it is unclear which extraocular muscle is causing anomalous eye movement or to what extent one of two muscles is responsible, temporary paralysis of the muscle with Xylocaine may provide the answer. The procedure is to inject 0.2 to 0.5 cc 2% Xylocaine directly into the muscle using electromyography (EMG) for precise localization, a technique similar to that of therapeutic injections of botulinum toxin (Oculinum). The procedure is especially useful for Duane's syndrome, superior oblique palsy, and other situations where abnormal muscle insertions or innervations make diagnosis of the muscle responsible for an eye movement anomaly difficult and surgery unpredictable.