Which Angle for which Surgical Strategy in Comitant Strabismus?

Abstract

Background

The fusion-free angle measured in the awake state was adopted as the angle of reference and the basis for conventional muscle surgery. The surgical effect is amount dependent.

Further analysis

The basic angle does not, however, correspond to the fusion-free angle in all types of comitant strabismus. In infantile esotropia it corresponds to the minimum angle. The difference between the maximum and the minimum angle represents the angle of variability. Weakening-reinforcing techniques (conventional surgery) to correct the minimum angle should therefore be combined with a progressive lessening technique (posterior fixation suture) to reduce the variability. In normosensorial strabismus the prism adaptation test, or prismotherapy, allows accurate determination of the basic angle to be corrected. The imbalance of the passive forces in an antagonistic muscle pair can be assessed during surgery under general anaesthesia in two ways, the eye position and the measurement of muscle extensibility. These two parameters are partially independent from the minimum angle measured in the awake state. The intraoperative data can, therefore, be considered as valuable parameters for adjusting the amount of conventional surgery.

Patients, method and results

A series of 80 children with infantile esotropia were operated on between 11 and 100 months of age. The surgical procedure consisted of bilateral posterior fixation sutures and uni- or bilateral medial rectus recessions. The intraoperative data were recorded in all cases. The amount of global recession was calculated on the minimum angle and adjusted if necessary during surgery according to the intraoperative data. The long-term results (follow-up of two years or more) show that the failures arose more often in the cases in which no adjustment was made.

Discussion and conclusion

An intraoperative adjustment of the amount of surgery is indicated according to the imbalance of passive muscle forces. Our long-term results, as yet uncompleted, suggest that the variance in results can be reduced by this strategy, along with taking into account the different angles of a deviation.

• Comitant strabismus
• surgical strategy
• basic angle
• minimum angle
• maximum angle
• passive forces imbalance
• anaesthesia