Succinyldicholine-induced return of the eyes to the basic deviation: a motion picture study

Change of Eye Position in Patients with Orthophoria and Horizontal Strabismus under General Anesthesia

We studied the relationship between eye position in the awakened state and in the surgical plane of anesthesia in orthophoric and horizontal strabismus patients. We classified 105 orthophoric and horizontal strabismus patients into 5 groups, measured the eye position at the primary position by photographic measurement of the corneal reflex positions and undertook a quantitative study of eye position. Under general anesthesia, the mean divergence was 39.7+/-8 PD for the esotropia group, 36.6+/-11.7 PD for exophoria, 27.4+/-8.1 PD for orthophoria, and 11.1+/-10.2 PD for exotropia I (< or =30 PD). Therefore, the esotropia group had the largest amount of divergence among the groups, but the eye position of the exotropia II (>30 PD) group was rather convergent at 11.0+/-6.5 PD. According to the eye position of the fixating and nonfixating eyes in the esotropia group, both eyes converged with an angle deviation of 14.4+/-4.8 PD divergent and 14.1+/-4.8 PD divergent, respectively (P=.71). In the exotropia groups (I, II), the fixating eye diverged but the nonfixating eye rather converged. Therefore, the angle deviation was 19.0+/-2.1 PD divergent for the fixating eye and 18.2+/-6.4 PD divergent for the nonfixating eye (P=.68). In conclusion, under general anesthesia, eye positions in the awakened state and in the surgical plane of anesthesia were convergent or divergent, and showed a tendency to converge into the position of 25-35 PD divergent. Therefore, we could not distinguish fixating eye from nonfixating eye under general anesthesia.

Quantitative forced ductions in an animal model--characterization of passive forces

PURPOSE

Our purpose was to characterize the passive tissue forces involved in ocular rotation in a controlled animal model and to evaluate the influence of manual versus mechanized ductions, repeated measurements, speed of rotation, and the influence of the nondepolarizing muscle relaxant mivacurium.

METHODS

Forced ductions were performed under general anesthesia on 20 eyes of 10 pigs, with or without mivacurium, with use of a highly sensitive force gauge attached to the eye by a traction suture. The eye was moved either manually or at constant speed with a motorized platform. Eyes were rotated a total of 8 mm from their resting position under anesthesia. The force-displacement relationship was analyzed and compared between groups.

RESULTS

A linear (elastic) relationship between force and displacement was noted, with a slope of 0.4 g per degree with use of the mechanized technique. Neither speed of rotation, use of mivacurium, nor repeated ductions significantly influenced the shape or slope of the relationship. Hysteresis averaged 2 to 4 g. Measurements performed with use of the motorized platform showed significantly improved reliability over those made manually.

CONCLUSIONS

The passive length-tension data correlate well with data reported by others in humans. Within a wide range of eye movement, this force is elastic in nature. For relatively low angular velocities, such as might be produced in smooth pursuit, the passive forces do not change appreciably with changes in velocity. The nondepolarizing muscle relaxant mivacurium has no effect on accurate performance of passive forced ductions under general anesthesia. Studies collecting quantitative data on passive orbital forces should be performed, when feasible, with an automated duction and recording apparatus.

Intraoperative succinylcholine and the postoperative eye alignment

In 99 patients undergoing strabismus surgery, an intravenous bolus of succinylcholine (Sch) was given after completion of the strabismus procedure. Reliable data were obtained in 53 patients. The interlimbal distance measured at 60 seconds after injection (VR60) was compared to the interlimbal distance at 1 and 6 weeks postoperatively, to evaluate the correlation between the drug-induced eye position under anesthesia and the awake-eye alignment postoperatively. Correlations were highest in patients undergoing symmetric recessions of the medial or lateral recti in primary horizontal strabismus. Confidence intervals of 0.8 to 1.2 were noted for both the esotropia and exotropia groups. Two patients experienced Sch-related complications of masseter spasm and prolonged apnea. Although infrequent, the potential gravity of the complications from Sch use and the currently enjoyed high rate of success in primary strabismus surgery suggest that these formulas not be used clinically. Nonetheless, the high correlations between the drug-induced and awake ocular position provide further support to the premise that the Sch sensitive fibers provide an important motor component to the awake eye position.

Succinylcholine-stimulated muscle tensions following botulinum injection in the domestic cat

Succinylcholine (SCh) selectively stimulates, and can therefore selectively assay, the multiple innervated (MI) fiber system of the extraocular muscles. Since botulinum-A toxin has been observed to induce changes in eye position in humans, SCh was used to assess the effect of botulinum-A on the SCh-sensitive MI fibers of extraocular muscles. Intravenous SCh infusion (40 micrograms-1 kg-1 min-1 was performed in the anesthetized domestic cat. Thirty-eight infusions were performed in 19 normal controls, measuring the peak tensions generated in the four horizontal and four vertical rectus muscles. Succinylcholine-stimulated muscle tensions (SSMT) were then repeated in nine animals, 4 weeks and 10 weeks following injection of botulinum-A toxin into both medial rectus muscles. Mean peak SSMTs were unchanged at 4 and 10 weeks following botulinum injection when compared to controls. We propose that botulinum chemo-denervation has no acute or chronic effect on the MI SCh-sensitive muscle fibers of the medial recti of the domestic cat. This lack of effect on the postsynaptic MI fibers indirectly supports light and electron microscopic studies which show changes predominantly in the singly innervated (SI), rather than the MI fibers following botulinum injection. Mean peak SSMTs were also greater for medial and superior rectus muscles compared to lateral and inferior recti respectively, suggesting a greater number or proportion of MI fibers in medial and superior recti.

Heterophoria as a Measure of Subjects’ Alertness during Recovery from General Anesthesia

The purpose of the study was to measure the influence of subjects’ alertness on heterophoria. An experimental group of 43 patients was measured with the Maddox Wing test for heterophoria. Exophoria was greater 1½, 2½, and 3½ hr. after the end of general anesthesia than at baseline level. Data for a control group of 25 did not vary on the Maddox Wing over four hours. The baseline level was not different between the two groups, so heterophoria as measured with the Maddox Wing can be used to evaluate subjects’ alertness during recovery from general anesthesia.

Heterophoria as a measure of subjects' alertness during recovery from general anesthesia

The purpose of the study was to measure the influence of subjects' alertness on heterophoria. An experimental group of 43 patients was measured with the Maddox Wing test for heterophoria. Exophoria was greater 1 1/2, 2 1/2, and 3 1/2 hr. after the end of general anesthesia than at baseline level. Data for a control group of 25 did not vary on the Maddox Wing over four hours. The baseline level was not different between the two groups, so heterophoria as measured with the Maddox Wing can be used to evaluate subjects' alertness during recovery from general anesthesia.

A comparison of the succinylcholine induced ocular position and the postoperative alignment in strabismus

Succinylcholine was injected intraoperatively in 41 strabismus patients with congenital esotropia or intermittent or constant exotropia. Regression analyses were performed to investigate the predictive relationships between the one-, six-, and 26-week postoperative alignment and the intraoperative, succinylcholine-induced ocular position. Ocular position, determined by the interlimbal distance in millimeters, was calculated using a semi-automated, video replay analysis system. Large, statistically significant correlation coefficients were obtained for patients undergoing bimedial recessions of 4.0 to 5.5 mm and bilateral lateral rectus recessions of 5.0 to 7.0 mm. Small correlations were obtained for esotropes undergoing the recession/resection procedure and those with bimedial recessions of 6.0 mm or greater. These data support the theory that the succinylcholine-sensitive subgroup of the extraocular muscle fibers are those whose tonic contracture provide the motor component to ocular alignment. Sample sizes at present are insufficient to suggest clinical use of these data. In future research, these relationships will be tested for their ability to predict postoperative alignment and thereby, improve success rates in strabismus surgery.

Succinylcholine as a predictor in strabismus surgery

Succinylcholine was injected intraoperatively in 20 patients with congenital esotropia, before and after the surgical procedure. Regression analysis was performed to investigate the relationship between the awake pre- and postoperative alignment and the drug-induced ocular positions, under anesthesia. The postoperative succinylcholine-induced ocular position was found to be a highly significant predictor of the one week postoperative alignment (r = 0.98, p less than 0.0001). Further investigation may lead to an ability to predict the postoperative alignment intraoperatively.

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.