According to one aspect, the fibers of a muscle to be shortened or lengthened are exposed to a local anesthetic drug such as bupivacaine. The concentration and volume of the local anesthetic drug are sufficient to causes the muscle fibers to be damaged by the myotoxicity of the drug. The muscle is then kept at a different length, shorter or longer, during the ensuing period of muscle fiber regeneration, resulting in a shortened or lengthened muscle. In one embodiment, the shortened length of the treated muscle improved the position and the movement of the eye to which it was attached.