Purpose: Incomplete transection of the inferior oblique muscle during myotomy or myectomy is an important preventable cause of ineffective inferior oblique weakening surgery. Intraoperative traction testing has been suggested as a means of detecting an incomplete inferior oblique transection. The usefulness of intraoperative traction testing to detect incomplete myotomy was evaluated.
Methods: The subjective "tightness" of the inferior oblique muscle was evaluated after partial and complete myotomy to determine how partial myotomy affected inferior oblique traction testing and to determine whether intraoperative traction testing is an effective means of ensuring that a complete myotomy has been achieved. Serial traction testing was performed on 10 inferior oblique muscles at the time of myotomy and scored, 0+ to 4+ tightness. Testing was performed before myotomy and after 50%, 90%, and total myotomy.
Results: In 8 of 10 eyes traction testing remained strongly positive until the inferior oblique muscle had been completely transected. The average inferior oblique muscle tightness of these eight muscles was +1.69 before myotomy and after 50% and 90% myotomy. The tightness decreased to 0 after 100% myotomy. In two cases no inferior oblique muscle could be detected after 50% and 90% myotomy, respectively. These two muscles had preoperative traction testing of +0.5 and +1.00, respectively.
Conclusions: Intraoperative traction testing is a practical and effective method of detecting incomplete inferior oblique myotomy/myectomy, but the test should be interpreted with caution in patients with loose premyotomy muscles.