Succinyldicholine and the basic ocular deviation

We measured the ocular positions of conscious and anesthetized subjects from photographs. We obtained the conscious basic horizontal deviation by using the cover-uncover test. Intravenously administered succinyldicholine chloride, 2 mg/kg of body weight returned the eyes of 15 anesthetized volunteers to positions that agreed well with those of their conscious horizontal basic deviations in the primary position. The mean ratio (± S.E.) calculated by dividing the horizontal interlimbal distance 90 seconds after drug injection by that of the same subject's horizontal interlimbal conscious basic deviation was 0.99 ± 0.01. This result supported the theory that the multiply innervated (en grappe) extraocular muscle fibers were responsible for the basic deviation. Macaca nemestrina monkeys and baboons proved to be unsuitable primate models for the human succinyldicholine response. In humans, the drug-induced ocular position was often vertically above or below the primary position. The associated horizontal deviation appeared to follow the physiologic V pattern, being more divergent if the eyes were rotated up and more convergent if the eyes were rotated down. In one third of the subjects this vertical deviation resulted in drug-induced horizontal interlimbal distances that disagreed by more than 5% with those of the conscious basic deviation in the primary position. This effect makes succinyldicholine of little value for making quantitative estimates of the amount of ocular muscle surgery to be performed during strabismus correction procedures. We injected succinyldicholine at the conclusion of strabismus surgery in eight subjects to determine if the drug-induced ocular positions would predict the postoperative results. The muscles operated on responded as though temporarily paretic. The drug-induced ocular positions bore no resemblance to the postoperative results.