Optimum timing of postoperative adjustment in a rabbit model of adjustable suture strabismus surgery

Strabismus surgeons disagree on the optimum timing of the postoperative adjustment in adjustable suture surgery. We compared the peak force necessary for adjustment at various postoperative times using a rabbit model. Twenty- four eyes of 12 rabbits underwent a superior rectus recession of 5 mm using a standard adjustable suture technique. The eyes were randomized to adjustment at 15 minutes, and at 6, 24, and 48 hours postoperatively. The peak force required to advance the muscle 3 mm was measured using a strain gauge. During each adjustment, the peak force was noted to be that required for initial disinsertion of muscle from sclera. The mean peak force required was 14 ± 5 g at 15 minute, 37 ± 10 g at 6 hours, 60 ± 40 g at 24 hours, and 103 ± 52 g at 48 hours. There was a significant relationship between the time of adjustment and the peak force required for adjustment (F=7.8, P=0.001). Post- hoc analysis showed that the peak force required at 48 hours was greater than that required at 24 hours (P=0.04), 6 hours (P=0.003), and at 15 minutes (P=0.0002). The force required for adjustment at 24 hours and beyond was greater than the maximal force generated by an extraocular muscle. We therefore suggest that the postoperative adjustment should be performed within the first 24 hours.