Objective: Pain from intraoperative retraction of extraocular muscles is the main cause of ocular discomfort after strabismus surgery. Injection of the long-acting local anesthetics can reduce ocular pain after strabismus surgery under general anesthesia.

Purpose: To evaluate the efficacy of subtenon bupivacaine injection on postoperative pain control

Materials: A prospective double-masked randomized trial was conducted in 18 eyes of 9 patients (age range 20-67 years) who underwent binocular strabismus surgery under general anesthesia at Thammasat hospital. Patients were randomly selected to receive subtenon injection with 0.5% bupivacaine 0.1 ml in one eye and sterile saline injection in fellow eye at the end of surgery. Primary outcome measures were visual rating pain scores at 30 minutes, 1 hour, 4 hours and 6 hours postoperatively. Secondary outcome measures were adverse effect of bupivacaine injection. Oral acetaminophen can be added up to the satisfaction of the patient. The doses of this adjunctive analgesia were recorded.

Results: Average pain score between study group vs control group was 1.33 vs 2.66, 1.44 vs 2.77,1 vs 1.66 and 0.3 vs 1.3 in the first 30 minutes, 1 hour, 4 hours and 6 hours, respectively. Pain scores at the first 6 hours postoperatively were significantly lower in study group (P=0.001).

Discussion: Adjunctive subtenon bupivacaine injection had effects at the first 6 hours postoperatively in adults undergoing strabismus surgery with general anesthesia technique.

Conclusion: Subtenon injection of bupivacaine may reduce postoperative pain score in adult strabismus surgery.