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

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.

Perianesthesia care of adult and pediatric strabismus surgery patients

Strabismus procedures on children and adults are frequently performed in an outpatient setting. Perianesthesia care of patients having strabismus procedures may be optimized by recognizing the characteristics of strabismus patients, the frequently associated diagnoses that may affect perioperative care, and the specific surgical techniques used to treat strabismus. Complications including postoperative nausea, pain, prolonged PACU stay, and unplanned postoperative admissions can be minimized and treatment facilitated by preparing patients with preoperative instructions, careful choice of anesthetic agents and postoperative medications, and appropriate perioperative care. This report will provide a brief review of surgical strabismus, including current techniques, and present guidelines for perioperative care of pediatric and adult strabismus patients.

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.

Reliability and variability in the measurement of interlimbal distance with a semiautomated video replay analysis system (SAVRAS)

This paper reports on the reliability and variability of a semi-automated, video replay and analysis system (SAVRAS) in determining interlimbal distance in patients with strabismus. Factors under investigation were: choice of observer, choice of video frame, patient age and patient state (awake or anesthetized). It was demonstrated that SAVRAS was a highly reliable and reproducible system. This system is currently in use to evaluate the relationship between the succinylcholine induced ocular position, under anesthesia, and the postoperative awake alignment.